Summary: Protein tyrosine kinase
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Tyrosine kinase Edit Wikipedia article
|Protein tyrosine kinase|
pdb 2HCK, rendered in PyMOL
A tyrosine kinase is an enzyme that can transfer a phosphate group from ATP to a protein in a cell. It functions as an "on" or "off" switch in many cellular functions. Tyrosine kinases are a subclass of protein kinase.
The phosphate group is attached to the amino acid tyrosine on the protein. Tyrosine kinases are a subgroup of the larger class of protein kinases that attach phosphate groups to other amino acids (serine and threonine). Phosphorylation of proteins by kinases is an important mechanism in communicating signals within a cell (signal transduction) and regulating cellular activity, such as cell division.
Protein kinases can become mutated, stuck in the "on" position, and cause unregulated growth of the cell, which is a necessary step for the development of cancer. Therefore, kinase inhibitors, such as imatinib, are often effective cancer treatments.
Most tyrosine kinases have an associated protein tyrosine phosphatase, which removes the phosphate group.
- 1 Reaction
- 2 Function
- 3 Regulation
- 4 Structure
- 5 Families
- 6 Clinical significance
- 7 Inhibitors
- 8 Examples
- 9 See also
- 10 References
- 11 External links
Protein kinases are a group of enzymes that possess a catalytic subunit that transfers the gamma (terminal) phosphate from nucleotide triphosphates (often ATP) to one or more amino acid residues in a protein substrate side-chain, resulting in a conformational change affecting protein function. The enzymes fall into two broad classes, characterised with respect to substrate specificity: serine/threonine-specific, and tyrosine-specific (the subject of this article).
The term kinase describes a large family of enzymes that are responsible for catalyzing the transfer of a phosphoryl group from a nucleoside triphosphate donor, such as ATP, to an acceptor molecule. Tyrosine kinases catalyze the phosphorylation of tyrosine residues in proteins. The phosphorylation of tyrosine residues in turn causes a change in the function of the protein that they are contained in.
Phosphorylation at tyrosine residues controls a wide range of properties in proteins such as enzyme activity, subcellular localization, and interaction between molecules. Furthermore, tyrosine kinases function in many signal transduction cascades wherein extracellular signals are transmitted through the cell membrane to the cytoplasm and often to the nucleus, where gene expression may be modified. Finally mutations can cause some tyrosine kinases to become constitutively active, a nonstop functional state that may contribute to initiation or progression of cancer.
Tyrosine kinases function in a variety of processes, pathways, and actions, and are responsible for key events in the body. The receptor tyrosine kinases function in transmembrane signaling, whereas tyrosine kinases within the cell function in signal transduction to the nucleus. Tyrosine kinase activity in the nucleus involves cell-cycle control and properties of transcription factors. In this way, in fact, tyrosine kinase activity is involved in mitogenesis, or the induction of mitosis in a cell; proteins in the cytosol and proteins in the nucleus are phosphorylated at tyrosine residues during this process. Cellular growth and reproduction may rely to some degree on tyrosine kinase. Tyrosine kinase function has been observed in the nuclear matrix, which comprises not the chromatin but rather the nuclear envelope and a “fibrous web” that serves to physically stabilize DNA. To be specific, Lyn, a type of kinase in the Src family that was identified in the nuclear matrix, appears to control the cell cycle. Src family tyrosine kinases are closely related but demonstrate a wide variety of functionality. Roles or expressions of Src family tyrosine kinases vary significantly according to cell type, as well as during cell growth and differentiation. Lyn and Src family tyrosine kinases in general have been known to function in signal transduction pathways. There is evidence that Lyn is localized at the cell membrane; Lyn is associated both physically and functionally with a variety of receptor molecules.
Fibroblasts – a type of cell that synthesizes the extracellular matrix and collagen and is involved in wound healing – that have been transformed by the polyomavirus possess higher tyrosine activity in the cellular matrix. Furthermore, tyrosine kinase activity has been determined to be correlated to cellular transformation. It has also been demonstrated that phosphorylation of a middle-T antigen on tyrosine is also associated with cell transformation, a change that is similar to cellular growth or reproduction.
The transmission of mechanical force and regulatory signals are quite fundamental in the normal survival of a living organism. Protein tyrosine kinase plays a role in this task, too. A protein tyrosine kinase called pp125 is likely at hand in the influence of cellular focal adhesions, as indicated by an immunofluorescent localization of the said kinase. Focal adhesions are macromolecular structures that function in the transmission of mechanical force and regulatory signals. Among the scientific community, pp125 is also referred to as FAK (focal adhesion kinase), due to its aforementioned presence in cellular focal adhesions. The protein tyrosine kinase pp125 is one of the major phosphotyrosine–containing proteins in unaffected (untransformed) avian and rodent fibroblast cells (fibroblast cells are explained above in some detail). Fibroblasts are a cell type responsible for wound healing and cell structure in animals, among a number of other relatively minor but important jobs that take place often or occasionally. The sequence and structure of pp125, when compared to National Biomedical Research Foundation and GenBank data bases, may be quite unique, meaning that it could be a new member of the protein tyrosine kinase family. This protein tyrosine kinase is up to about 70% unique compared to some other protein tyrosine kinases, a figure that is unlike those between actual members of an established protein tyrosine kinase family. Also, the amino acid sequence that was observed indirectly signifies that it is associated with the cytoplasm, dubbing it one in a large group of cytoplasmic protein tyrosine kinases. It was discovered when monoclonal antibodies were observed to recognize it. Monoclonal antibodies, from chicken embryo cells transformed by pp60v-src, recognize seven different phosphotyrosine-containing proteins. One of these monoclonal antibodies, named 2A7, recognizes pp125, support for the idea that pp125 is, in fact, a protein tyrosine kinase.
Cellular proliferation, as explained in some detail above, may rely in some part on tyrosine kinase. Tyrosine kinase function has been observed in the nuclear matrix. Lyn, the type of kinase that was the first to be discovered in the nuclear matrix, is part of Src family of tyrosine kinases, which can be contained in the nucleus of differentiating, calcium-provoked kertinocytes. Lyn, in the nuclear matrix, among the nuclear envelope and the “fibrous web” that physically stabilizes DNA, was found functioning in association with the matrix. Also, it appeared to be conditional to cell cycle. The contribution of the Lyn protein to the total tyrosine kinase activity within the nuclear matrix is unknown, however; because the Lyn was extracted only partially, an accurate measurement of its activity could not be managed. Indications, as such, are that, according to Vegesna et al. (1996), Lyn polypeptides are associated with tyrosine kinase activity in the nuclear matrix. The extracted Lyn was enzymatically active, offering support for this notion.
Yet another possible and probable role of protein tyrosine kinase is that in the event of circulatory failure and organ dysfunction caused by endotoxin in rats, where the effects of inhibitors tyrphostin and genistein are involved with protein tyrosine kinase. Signals in the surroundings received by receptors in the membranes of cells are transmitted into the cell cytoplasm. Transmembrane signaling due to receptor tyrosine kinases, according to Bae et al. (2009), relies heavily on interactions, for example, mediated by the SH2 protein domain; it has been determined via experimentation that the SH2 protein domain selectivity is functional in mediating cellular processes involving tyrosine kinase. Receptor tyrosine kinases may, by this method, influence growth factor receptor signaling. This is one of the more fundamental cellular communication functions metazoans.
Major changes are sometimes induced when the tyrosine kinase enzyme is affected by other factors. One of the factors is a molecule that is bound reversibly by a protein, called a ligand. A number of receptor tyrosine kinases, though certainly not all, do not perform protein-kinase activity until they are occupied, or activated, by one of these ligands. It is interesting to note that, although many more recent cases of research indicate that receptors remain active within endosomes, it was once thought that endocytosis caused by ligands was the event responsible for the process in which receptors are inactivated. Activated receptor tyrosine kinase receptors are internalized (recycled back into the system) in short time and are ultimately delivered to lysosomes, where they become work-adjacent to the catabolic acid hydrolases that partake in digestion. Internalized signaling complexes are involved in different roles in different receptor tyrosine kinase systems, the specifics of which were researched. In addition, ligands participate in reversible binding, a term that describes those inhibitors that bind non-covalently (inhibition of different types are effected depending on whether these inhibitors bind the enzyme, the enzyme-substrate complex, or both). Multivalency, which is an attribute that bears particular interest to some people involved in related scientific research, is a phenomenon characterized by the concurrent binding of several ligands positioned on one unit to several coinciding receptors on another. In any case, the binding of the ligand to its partner is apparent owing to the effects that it can have on the functionality of many proteins. Ligand-activated receptor tyrosine kinases, as they are sometimes referred to, demonstrate a unique attribute. Once a tyrosine receptor kinase is bonded to its ligand, it is able to bind to tyrosine kinase residing in the cytosol of the cell.
Erythrocytes as an example
An example of this trigger-system in action is the process by which the formation of erythrocytes is regulated. Mammals possess this system, which begins in the kidneys where the developmental signal is manufactured. The developmental signal, also called a cytokine, is erythropoietin in this case. (Cytokines are key regulators of hematopoietic cell proliferation and differentiation.) Erythropoietin's activity is initiated when hematopoietic cytokine receptors become activated. In erythrocyte regulation, erythropoietin is a protein containing 165 amino acids that plays a role in activating the cytoplasmic protein kinase JAK. The results of some newer research have also indicated that the aforementioned cytokine receptors function with members of the JAK tyrosine kinase family. The cytokine receptors activate the JAK kinases. This then results in the phosphorylation of several signaling proteins located in the cell membrane. This subsequently affects both the stimulation of ligand-mediated receptors and intracellular signaling pathway activation. Substrates for JAK kinases mediate some gene responses and more. The process is also responsible for mediating the production of blood cells. In this case, erythropoietin binds to the corresponding plasma membrane receptor, dimerizing the receptor. The dimer is responsible for activating the kinase JAK via binding. Tyrosine residues located in the cytoplasmic domain of the erythropoietin receptor are consequently phosphorylated by the activated protein kinase JAK. Overall, this is also how a receptor tyrosine kinase might be activated by a ligand to regulate erythrocyte formation.
Additional instances of factor-influenced protein tyrosine kinase activity, similar to this one, exist. An adapter protein such as Grb2 will bind to phosphate-tyrosine residues under the influence of receptor protein kinases. This mechanism is an ordinary one that provokes protein-protein interactions.
Furthermore, to illustrate an extra circumstance, insulin-associated factors have been determined to influence tyrosine kinase. Insulin receptor substrates are molecules that function in signaling by regulating the effects of insulin. Many receptor enzymes have closely related structure and receptor tyrosine kinase activity, and it is said by Lehninger (2008) that the foundational or prototypical receptor enzyme, is insulin. It is interesting to note that insulin receptor substrates IRS2 and IRS3 each have unique characteristic tissue function and distribution that serves to enhance signaling capabilities in pathways that are initiated by receptor tyrosine kinases. Activated IRS-1 molecules enhance the signal created by insulin. The insulin receptor system, in contrast, appears to diminish the efficacy of endosomal signaling.
The epidermal growth factor receptor system, as such, has been used as an intermediate example. Some signals are produced from the actual cell surface in this case but other signals seem to emanate from within the endosomes. This variety of function may be a means to create ligand-specific signals. This supports the notion that trafficking, a term for the modification of proteins subsequent to mRNA translation, may be vital to the function of receptor signaling.
Included in a number of the structural features that can be recognized in all protein tyrosine kinases are an ATP binding site, three residues that are thought to be associated with the function of the third phosphate group (often called the gamma-phosphate group) of an ATP molecule bound to the enzyme, and a possible catalytic site of the enzyme that is an amino acid. Also very common among protein tyrosine kinases are two peptide sequences.
The tyrosine kinases are divided into two main families:
Approximately 2000 kinases are known, and more than 90 Protein Tyrosine Kinases (PTKs) have been found in the human genome. They are divided into two classes, receptor and non-receptor PTKs.
By 2004, 58 receptor tyrosine kinases (RTKs) were known, grouped into 20 subfamilies. They play pivotal roles in diverse cellular activities including growth (by signaling neurotrophins), differentiation, metabolism, adhesion, motility, death. RTKs are composed of an extracellular domain, which is able to bind a specific ligand, a transmembrane domain, and an intracellular catalytic domain, which is able to bind and phosphorylate selected substrates. Binding of a ligand to the extracellular region causes a series of structural rearrangements in the RTK that lead to its enzymatic activation. In particular, movement of some parts of the kinase domain gives free access to adenosine triphosphate (ATP) and the substrate to the active site. This triggers a cascade of events through phosphorylation of intracellular proteins that ultimately transmit ("transduce") the extracellular signal to the nucleus, causing changes in gene expression. Many RTKs are involved in oncogenesis, either by gene mutation, or chromosome translocation, or simply by over-expression. In every case, the result is a hyper-active kinase, that confers an aberrant, ligand-independent, non-regulated growth stimulus to the cancer cells.
The first non-receptor tyrosine kinase identified was the v-src oncogenic protein. Most animal cells contain one or more members of the Src family of tyrosine kinases. A chicken sarcoma virus was found to carry mutated versions of the normal cellular Src gene. The mutated v-src gene has lost the normal built-in inhibition of enzyme activity that is characteristic of cellular SRC (c-src) genes. SRC family members have been found to regulate many cellular processes. For example, the T-cell antigen receptor leads to intracellular signalling by activation of Lck and Fyn, two proteins that are structurally similar to Src.
Tyrosine kinases are particularly important today because of their implications in the treatment of cancer. A mutation that causes certain tyrosine kinases to be constitutively active has been associated with several cancers. Imatinib (brand names Gleevec and Glivec) is a drug able to bind the catalytic cleft of these tyrosine kinases, inhibiting its activity.
Tyrosine kinase activity is also significantly involved in other events that are sometimes considered highly unfavorable. For instance, enhanced activity of the enzyme has been implicated in the derangement of the function of certain systems, such as cell division. Also included are numerous diseases related to local inflammation such as atherosclerosis and psoriasis, or systemic inflammation such as sepsis and septic shock. A number of viruses target tyrosine kinase function during infection. The polyoma virus affects tyrosine kinase activity inside the nuclear matrix. Fibroblasts are cells involved in wound healing and cell structure formation in mammalian cells. When these cells are transformed by the polyoma virus, higher tyrosine activity is observed in the cellular matrix, which is also correlated to cellular proliferation. Another virus that targets tyrosine kinase is the Rous sarcoma virus, a retrovirus that causes sarcoma in chickens. Infected cells display obvious structure modifications and cell growth regulation that is extremely unusual. Protein tyrosine kinases that are encoded by the Rous sarcoma virus cause cellular transformation, and are termed oncoproteins. In addition, tyrosine kinase can sometimes function incorrectly in such a way that leads to non-small cell lung cancer. A common, widespread cancer, non-small cell lung cancer is the cause of death in more people than the total number in breast, colorectal, and prostate cancer together.
Research has shown that protein phosphorylation occurs on residues of tyrosine by both transmembrane receptor- and membrane-associated protein tyrosine kinases in normal cells. Phosphorylation plays a significant role in cellular signalling that regulates the number and variety of growth factors. This is evidenced by the observation that cells affected by the Rous sarcoma virus display obvious structural modifications and a total lack of normal cell growth regulation. Rous sarcoma virus-encoded oncoproteins are protein tyrosine kinases that are the cause of, and are required for, this cellular transformation. Tyrosine phosphorylation activity also increases or decreases in conjunction with changes in cell composition and growth regulation. In this way, a certain transformation exhibited by cells is dependent on a role that tyrosine kinase demonstrates. Protein tyrosine kinases, have a major role in the activation of lymphocytes. In addition, they are functional in mediating communication pathways in cell types such as adrenal chromaffin, platelets, and neural cells.
A tyrosine kinase can become an unregulated enzyme within an organism due to influences discussed, such as mutations and more. This behavior causes havoc; essential processes become disorganized. Systems on which the organism relies malfunction, resulting often in cancers. Preventing this type of circumstance is highly desirable. Much research has already noted the significant effect that inhibitors of the radically functioning protein tyrosine kinase enzymes have on related ailments. (See Tyrosine-kinase inhibitor )
Non-small cell lung cancer
Cancer’s response to an inhibitor of tyrosine kinase was assessed in a clinical trial. In this case, Gefitinib is the inhibitor of tyrosine kinase. Incorrect tyrosine kinase function can lead to non-small cell lung cancer. Gefitinib is a tyrosine kinase inhibitor that targets the epidermal growth factor receptor, inducing favorable outcomes in patients with non-small cell lung cancers. A common, widespread cancer, non-small cell lung cancer is the cause of death in more people than breast, colorectal, and prostate cancer together. This is strong motivation to perform research on tyrosine kinase inhibitors as potential targets in cancer treatment. Gefitinib, functioning as an epidermal growth factor receptor tyrosine kinase inhibitor, improved symptoms related to non-small cell lung cancer and resulted in radiographic tumor regressions. This is an example of the efficacy of such an inhibitor. The process of inhibition shows how the cancer sustains. Mutations in the epidermal growth factor receptor activate signalling pathways that promote cell survival. Non-small cell lung cancer cells become dependent on these survival signals. Gefitinib’s inhibition of the survival signals may be a contributing factor to its efficacy as a drug for non-small cell cancer treatment.
Gefitinib is well endured by humans, and treatment resulted in a symptom improvement rate of 43% (with 95% confidence in a 33%–53% interval) for patients that received 250 mg of Gefitinib and 35% (with 95% confidence in a 26%–45% interval) for those that received 500 mg. In the trial, epidermal growth factor receptor showed a rapid response to the inhibitor, as demonstrated by the improvement of the cancer symptoms. In each group, improvements were noted after a single week of epidermal growth factor receptor tyrosine kinase inhibitor treatment. Gefitinib application once per day caused “rapid” symptom improvement and tumor regressions in non-small cell lung cancer patients. In the field of medical research, this is an especially significant example of the use of an inhibitor to treat tyrosine kinase-associated cancer. Chemotherapy, surgery, and radiotherapy were the only major options available prior to the discoveries made in this trial. The side-effects of Gefitinib oral treatment once per day were considered significant. Diarrhea was reported in 57% of patients in the 250 mg group and in 75% of the 500 mg group. One patient had diarrhea more severe than Grade 2, with up to six bowel movements in only one day. Also, a death occurred possibly due to epidermal growth factor receptor tyrosine kinase inhibitor treatment; however, the correlation is not exactly clear. In addition, skin toxicity was observed in 62% of patients in the 250 mg group. Nevertheless, the side-effects of Gefitinib were only “generally mild, manageable, noncumulative, and reversible.” Unfortunately, ceasing to take the inhibitor may be the only reversal strategy of the unfavorable symptoms. Gefitinib still represents a reasonably safe and effective treatment compared to other cancer therapies.
Furthermore, epidermal growth factor receptor plays a crucial role in tumorigenesis, which is the production of a new tumor. By 2010 Two monoclonal antibodies and another small-molecule tyrosine kinase inhibitor called Erlotinib had also been developed to treat cancer.
July 12, 2013 FDA approved afatinib "multiple recepptor, irreversible TKI" for the first-line treatment of patients with metastatic non-small cell lung cancer (NSCLC) whose tumors have epidermal growth factor receptor (EGFR) mutation
Chronic myeloid leukemia
BCR-ABL is a constitutively activated tyrosine kinase that is associated with chronic myeloid leukemia. Tyrosine kinase activity is crucial for the transformation of BCR-ABL. Therefore, inhibiting it improves cancer symptoms. Among currently available inhibitors to treat CML are imatinib, dasatinib, nilotinib, bosutinib and ponatinib.
Gastrointestinal stromal tumors
Gastrointestinal stromal tumors (GIST) are known to withstand cancer chemotherapy treatment and do not respond to any kind of therapy (in 2001) in advanced cases. However, tyrosine kinase inhibitor STI571 (imatinib) is effective in the treatment of patients with metastatic gastrointestinal stromal tumors. Gastrointestinal stromal tumors consist of a cluster of mesenchymal neoplasms that are formed from precursors to cells that make up the connective-tissue in the gastrointestinal tract. Most of these tumors are found in the stomach, though they can also be located in the small intestine or elsewhere in the intestinal tract. The cells of these tumors have a growth factor receptor associated with tyrosine kinase activity. This growth factor receptor is called c-kit and is produced by a proto-oncogene (c-kit). Mutation of c-kit causes the constitutive activity of tyrosine kinase, which results in cancerous gastrointestinal stromal tumors. Results of c-kit mutation include unrestricted tyrosine kinase activity and cell proliferation, unregulated phosphorylation of c-kit, and disruption of some communication pathways. Therapy with imatinib can inhibit the non-normal cell signaling mechanisms in gastrointestinal stromal tumors. This results in significant responses in patients and sustained disease control. By 2001 it was no longer doubted that this inhibitor can be effective and safe in humans. In similar manner, protein tyrosine kinase inhibitor STI571 was found to significantly reduce the physical size of tumors; they decreased roughly 65% in size in 4 months of trialing, and continued to diminish. New lesions did not appear, and a number of the liver metastases completely reduced to non-existence. The single patient in the study remained healthy following treatment. There are no effective means of treatment for advanced gastrointestinal stromal tumors, but that STI571 represents an effective treatment in early stage cancer associated with constitutively active c-kit, by inhibiting unfavourable tyrosine kinase activity.
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To reduce enzyme activity, inhibitor molecules bind to enzymes. Reducing enzyme activity can disable a pathogen or correct an incorrectly function system; as such, many enzyme inhibitors are developed to be used as drugs for the general public.
GIST and Imatinib
Gastrointestinal stromal tumors (GIST) are mesenchymal tumors that affect the gastrointestinal tract. Treatment options have been limited. However Imatinib, as an inhibitor to the malfunctioning enzyme, can be effective.
Chronic myelogenous leukemia and nilotinib
If imatinib does not work, patients with advanced chronic myelogenous leukemia can use nilotinib, dasatinib, bosutinib, ponatinib, or another inhibitor to the malfunction enzyme that causes the leukemia. This inhibitor is a highly selective Bcr-Abl tyrosine kinase inhibitor.
Sunitinib is an oral tyrosine kinase inhibitor that acts upon vascular endothelial growth factor receptor (VEGFR), platelet-derived growth factor receptor (PDGFR), stem cell factor receptor, and colony-stimulating factor-1 receptor (Burstein et al. 2008)
Gefitinib and erlotinib inhibit the tyrosine kinase domain of epidermal growth factor receptor (EGFR), and can be used to treat lung and pancreatic cancer where there is often over-expression of this cell-surface receptor tyrosine kinase.
Kinase inhibitors can also be mediated. Paracrine signalling mediates the response to epidermal growth factor receptor kinase inhibitors. Paracrine activates epidermal growth factor receptor in endothelial cells of the tumor to do this.
Human proteins containing this domain include:
AATK; ABL; ABL2; ALK; AXL; BLK; BMX; BTK; CSF1R; CSK; DDR1; DDR2; EGFR; EPHA1; EPHA2; EPHA3; EPHA4; EPHA5; EPHA6; EPHA7; EPHA8; EPHA10; EPHB1; EPHB2; EPHB3; EPHB4; EPHB6; ERBB2; ERBB3; ERBB4; FER; FES; FGFR1; FGFR2; FGFR3; FGFR4; FGR; FLT1; FLT3; FLT4; FRK; FYN; GSG2; HCK; IGF1R; ILK; INSR; INSRR; IRAK4; ITK; JAK1; JAK2; JAK3; KDR; KIT; KSR1; LCK; LMTK2; LMTK3; LTK; LYN; MATK; MERTK; MET; MLTK; MST1R; MUSK; NPR1; NTRK1; NTRK2; NTRK3; PDGFRA; PDGFRB; PLK4; PTK2; PTK2B; PTK6; PTK7; RET; ROR1; ROR2; ROS1; RYK; SGK493; SRC; SRMS; STYK1; SYK; TEC; TEK; TEX14; TIE1; TNK1; TNK2; TNNI3K; TXK; TYK2; TYRO3; YES1; ZAP70
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No Pfam abstract.
Hanks SK, Quinn AM; , Methods Enzymol 1991;200:38-62.: Protein kinase catalytic domain sequence database: identification of conserved features of primary structure and classification of family members. PUBMED:1956325 EPMC:1956325
Internal database links
|SCOOP:||ABC1 APH Choline_kinase EcKinase Fructosamin_kin FTA2 Haspin_kinase Imm7 Kdo Kinase-like PIP49_C Pkinase Pox_ser-thr_kin RIO1 Seadorna_VP7 WaaY YrbL-PhoP_reg YukC|
|Similarity to PfamA using HHSearch:||Pkinase Haspin_kinase FTA2 Kinase-like|
External database links
|PROSITE:||PDOC00100 PDOC00212 PDOC00213 PDOC00629|
This tab holds annotation information from the InterPro database.
InterPro entry IPR001245
Protein phosphorylation, which plays a key role in most cellular activities, is a reversible process mediated by protein kinases and phosphoprotein phosphatases. Protein kinases catalyse the transfer of the gamma phosphate from nucleotide triphosphates (often ATP) to one or more amino acid residues in a protein substrate side chain, resulting in a conformational change affecting protein function. Phosphoprotein phosphatases catalyse the reverse process. Protein kinases fall into three broad classes, characterised with respect to substrate specificity [PUBMED:3291115]:
- Serine/threonine-protein kinases
- Tyrosine-protein kinases
- Dual specificity protein kinases (e.g. MEK - phosphorylates both Thr and Tyr on target proteins)
Protein kinase function is evolutionarily conserved from Escherichia coli to human [PUBMED:12471243]. Protein kinases play a role in a multitude of cellular processes, including division, proliferation, apoptosis, and differentiation [PUBMED:12368087]. Phosphorylation usually results in a functional change of the target protein by changing enzyme activity, cellular location, or association with other proteins. The catalytic subunits of protein kinases are highly conserved, and several structures have been solved [PUBMED:15078142], leading to large screens to develop kinase-specific inhibitors for the treatments of a number of diseases [PUBMED:15320712].This entry represents the catalytic domain found in a number of serine/threonine- and tyrosine-protein kinases. It does not include catalytic domain of dual specificity kinases.
The mapping between Pfam and Gene Ontology is provided by InterPro. If you use this data please cite InterPro.
|Molecular function||protein kinase activity (GO:0004672)|
|Biological process||protein phosphorylation (GO:0006468)|
Below is a listing of the unique domain organisations or architectures in which this domain is found. More...
The graphic that is shown by default represents the longest sequence with a given architecture. Each row contains the following information:
- the number of sequences which exhibit this architecture
a textual description of the architecture, e.g. Gla, EGF x 2, Trypsin.
This example describes an architecture with one
Gladomain, followed by two consecutive
EGFdomains, and finally a single
- a link to the page in the Pfam site showing information about the sequence that the graphic describes
- the UniProt description of the protein sequence
- the number of residues in the sequence
- the Pfam graphic itself.
Note that you can see the family page for a particular domain by clicking on the graphic. You can also choose to see all sequences which have a given architecture by clicking on the Show link in each row.
Finally, because some families can be found in a very large number of architectures, we load only the first fifty architectures by default. If you want to see more architectures, click the button at the bottom of the page to load the next set.
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This superfamily includes the Serine/Threonine- and Tyrosine- protein kinases as well as related kinases that act on non-protein substrates.
The clan contains the following 35 members:ABC1 AceK Act-Frag_cataly Alpha_kinase APH APH_6_hur Choline_kinase CotH DUF1679 DUF2252 DUF4135 EcKinase Fam20C Fructosamin_kin FTA2 Haspin_kinase HipA_C Ins_P5_2-kin IPK IucA_IucC Kdo Kinase-like KIND PI3_PI4_kinase PIP49_C PIP5K Pkinase Pkinase_Tyr Pox_ser-thr_kin RIO1 Seadorna_VP7 UL97 WaaY YrbL-PhoP_reg YukC
We store a range of different sequence alignments for families. As well as the seed alignment from which the family is built, we provide the full alignment, generated by searching the sequence database (reference proteomes) using the family HMM. We also generate alignments using four representative proteomes (RP) sets, the UniProtKB sequence database, the NCBI sequence database, and our metagenomics sequence database. More...
There are various ways to view or download the sequence alignments that we store. We provide several sequence viewers and a plain-text Stockholm-format file for download.
We make a range of alignments for each Pfam-A family:
- the curated alignment from which the HMM for the family is built
- the alignment generated by searching the sequence database using the HMM
- Representative Proteomes (RPs) at 15%, 35%, 55% and 75% co-membership thresholds
- alignment generated by searching the UniProtKB sequence database using the family HMM
- alignment generated by searching the NCBI sequence database using the family HMM
- alignment generated by searching the metagenomics sequence database using the family HMM
You can see the alignments as HTML or in three different sequence viewers:
- a Java applet developed at the University of Dundee. You will need Java installed before running jalview
- an HTML page showing the whole alignment.Please note: full Pfam alignments can be very large. These HTML views are extremely large and often cause problems for browsers. Please use either jalview or the Pfam viewer if you have trouble viewing the HTML version
- an HTML-based representation of the alignment, coloured according to the posterior-probability (PP) values from the HMM. As for the standard HTML view, heatmap alignments can also be very large and slow to render.
You can download (or view in your browser) a text representation of a Pfam alignment in various formats:
You can also change the order in which sequences are listed in the alignment, change how insertions are represented, alter the characters that are used to represent gaps in sequences and, finally, choose whether to download the alignment or to view it in your browser directly.
You may find that large alignments cause problems for the viewers and the reformatting tool, so we also provide all alignments in Stockholm format. You can download either the plain text alignment, or a gzipped version of it.
We make a range of alignments for each Pfam-A family. You can see a description of each above. You can view these alignments in various ways but please note that some types of alignment are never generated while others may not be available for all families, most commonly because the alignments are too large to handle.
1Cannot generate PP/Heatmap alignments for seeds; no PP data available
Key: available, not generated, — not available.
Format an alignment
We make all of our alignments available in Stockholm format. You can download them here as raw, plain text files or as gzip-compressed files.
You can also download a FASTA format file containing the full-length sequences for all sequences in the full alignment.
HMM logos is one way of visualising profile HMMs. Logos provide a quick overview of the properties of an HMM in a graphical form. You can see a more detailed description of HMM logos and find out how you can interpret them here. More...
If you find these logos useful in your own work, please consider citing the following article:
This page displays the phylogenetic tree for this family's seed alignment. We use FastTree to calculate neighbour join trees with a local bootstrap based on 100 resamples (shown next to the tree nodes). FastTree calculates approximately-maximum-likelihood phylogenetic trees from our seed alignment.
Note: You can also download the data file for the tree.
Curation and family details
This section shows the detailed information about the Pfam family. You can see the definitions of many of the terms in this section in the glossary and a fuller explanation of the scoring system that we use in the scores section of the help pages.
|Number in seed:||122|
|Number in full:||68047|
|Average length of the domain:||230.00 aa|
|Average identity of full alignment:||24 %|
|Average coverage of the sequence by the domain:||35.37 %|
|HMM build commands:||
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 26740544 -E 1000 --cpu 4 HMM pfamseq
|Family (HMM) version:||16|
|Download:||download the raw HMM for this family|
Weight segments by...
Change the size of the sunburst
selected sequences to HMM
a FASTA-format file
- 0 sequences
- 0 species
This visualisation provides a simple graphical representation of the distribution of this family across species. You can find the original interactive tree in the More....
This chart is a modified "sunburst" visualisation of the species tree for this family. It shows each node in the tree as a separate arc, arranged radially with the superkingdoms at the centre and the species arrayed around the outermost ring.
How the sunburst is generated
The tree is built by considering the taxonomic lineage of each sequence that has a match to this family. For each node in the resulting tree, we draw an arc in the sunburst. The radius of the arc, its distance from the root node at the centre of the sunburst, shows the taxonomic level ("superkingdom", "kingdom", etc). The length of the arc represents either the number of sequences represented at a given level, or the number of species that are found beneath the node in the tree. The weighting scheme can be changed using the sunburst controls.
In order to reduce the complexity of the representation, we reduce the number of taxonomic levels that we show. We consider only the following eight major taxonomic levels:
Colouring and labels
Segments of the tree are coloured approximately according to their superkingdom. For example, archeal branches are coloured with shades of orange, eukaryotes in shades of purple, etc. The colour assignments are shown under the sunburst controls. Where space allows, the name of the taxonomic level will be written on the arc itself.
As you move your mouse across the sunburst, the current node will be highlighted. In the top section of the controls panel we show a summary of the lineage of the currently highlighed node. If you pause over an arc, a tooltip will be shown, giving the name of the taxonomic level in the title and a summary of the number of sequences and species below that node in the tree.
Anomalies in the taxonomy tree
There are some situations that the sunburst tree cannot easily handle and for which we have work-arounds in place.
Missing taxonomic levels
Some species in the taxonomic tree may not have one or more of the main eight levels that we display. For example, Bos taurus is not assigned an order in the NCBI taxonomic tree. In such cases we mark the omitted level with, for example, "No order", in both the tooltip and the lineage summary.
Unmapped species names
The tree is built by looking at each sequence in the full alignment for the family. We take the name of the species given by UniProt and try to map that to the full taxonomic tree from NCBI. In some cases, the name chosen by UniProt does not map to any node in the NCBI tree, perhaps because the chosen name is listed as a synonym or a misspelling in the NCBI taxonomy.
So that these nodes are not simply omitted from the sunburst tree, we group them together in a separate branch (or segment of the sunburst tree). Since we cannot determine the lineage for these unmapped species, we show all levels between the superkingdom and the species as "uncategorised".
Since we reduce the species tree to only the eight main taxonomic levels, sequences that are mapped to the sub-species level in the tree would not normally be shown. Rather than leave out these species, we map them instead to their parent species. So, for example, for sequences belonging to one of the Vibrio cholerae sub-species in the NCBI taxonomy, we show them instead as belonging to the species Vibrio cholerae.
Too many species/sequences
For large species trees, you may see blank regions in the outer layers of the sunburst. These occur when there are large numbers of arcs to be drawn in a small space. If an arc is less than approximately one pixel wide, it will not be drawn and the space will be left blank. You may still be able to get some information about the species in that region by moving your mouse across the area, but since each arc will be very small, it will be difficult to accurately locate a particular species.
The tree shows the occurrence of this domain across different species. More...
We show the species tree in one of two ways. For smaller trees we try to show an interactive representation, which allows you to select specific nodes in the tree and view them as an alignment or as a set of Pfam domain graphics.
Unfortunately we have found that there are problems viewing the interactive tree when the it becomes larger than a certain limit. Furthermore, we have found that Internet Explorer can become unresponsive when viewing some trees, regardless of their size. We therefore show a text representation of the species tree when the size is above a certain limit or if you are using Internet Explorer to view the site.
If you are using IE you can still load the interactive tree by clicking the "Generate interactive tree" button, but please be aware of the potential problems that the interactive species tree can cause.
For all of the domain matches in a full alignment, we count the number that are found on all sequences in the alignment. This total is shown in the purple box.
We also count the number of unique sequences on which each domain is found, which is shown in green. Note that a domain may appear multiple times on the same sequence, leading to the difference between these two numbers.
Finally, we group sequences from the same organism according to the NCBI code that is assigned by UniProt, allowing us to count the number of distinct sequences on which the domain is found. This value is shown in the pink boxes.
We use the NCBI species tree to group organisms according to their taxonomy and this forms the structure of the displayed tree. Note that in some cases the trees are too large (have too many nodes) to allow us to build an interactive tree, but in most cases you can still view the tree in a plain text, non-interactive representation. Those species which are represented in the seed alignment for this domain are highlighted.
You can use the tree controls to manipulate how the interactive tree is displayed:
- show/hide the summary boxes
- highlight species that are represented in the seed alignment
- expand/collapse the tree or expand it to a given depth
- select a sub-tree or a set of species within the tree and view them graphically or as an alignment
- save a plain text representation of the tree
Please note: for large trees this can take some time. While the tree is loading, you can safely switch away from this tab but if you browse away from the family page entirely, the tree will not be loaded.
There are 13 interactions for this family. More...
We determine these interactions using iPfam, which considers the interactions between residues in three-dimensional protein structures and maps those interactions back to Pfam families. You can find more information about the iPfam algorithm in the journal article that accompanies the website.
For those sequences which have a structure in the Protein DataBank, we use the mapping between UniProt, PDB and Pfam coordinate systems from the PDBe group, to allow us to map Pfam domains onto UniProt sequences and three-dimensional protein structures. The table below shows the structures on which the Pkinase_Tyr domain has been found. There are 1877 instances of this domain found in the PDB. Note that there may be multiple copies of the domain in a single PDB structure, since many structures contain multiple copies of the same protein seqence.
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