Summary: Restriction endonuclease BamHI
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BamHI Edit Wikipedia article
Restriction endonuclease BamH I bound to a non-specific DNA.
BamH I (from Bacillus amyloliquefaciens) is a type II restriction endonuclease, having the capacity for recognizing short sequences (6 b.p.) of DNA and specifically cleaving them at a target site. This exhibit focuses on the structure-function relations of BamH I as described by Newman, et al. (1995). BamH I binds at the recognition sequence 5'-GGATCC-3', and cleaves these sequences just after the 5'-guanine on each strand. This cleavage results in sticky ends which are 4 b.p. long. In its unbound form, BamH I displays a central b sheet, which resides in between a helices. BamH I is an extraordinarily unique molecule in that it undergoes a series of unconventional conformational changes upon DNA recognition. This allows the DNA to maintain its normal B-DNA conformation without distorting to facilitate enzyme binding. BamH I is a symmetric dimer. DNA is bound in a large cleft that is formed between dimers; the enzyme binds in a "crossover" manner. Each BamH I subunit makes the majority of its backbone contacts with the phosphates of a DNA half site but base pair contacts are made between each BamH I subunit and nitrogenous bases in the major groove of the opposite DNA half site. The protein binds the bases through either direct hydrogen bonds or water-mediated H-bonds between the protein and every H-bond donor/acceptor group in the major groove. Major groove contacts are formed by atoms residing on the amino-terminus of a parallel 4 helix bundle. This bundle marks the BamH I dimer interface, and it is thought that the dipole moments of the NH2-terminal atoms on this bundle may contribute to electrostatic stabilization.
Sites of Recognition Between BamH I and DNA
The BamH I enzyme is capable of making a large number of contacts with DNA. Water-mediated hydrogen bonding, as well as both main-chain and side-chain interactions aid in binding of the BamH I recognition sequence. In the major groove, the majority of enzyme/DNA contacts take place at the amino terminus of the parallel-4-helix bundle, made up of a4 and a6 from each subunit. Although a6 from each subunit does not enter the DNA major groove, its preceding loops interact with the outer ends of the recognition site. Conversely, a4 from each subunit does enter the major groove in the center of the recognition sequence. A total of 18 bonds are formed between the enzyme and DNA across the 6 base pair recognition sequence (12 direct and 6 water mediated bonds). As discussed above, the L and R subunits bind in a cross over manner, whereby the R-subunit of BamH I contacts the left DNA half-site of the recognition sequence. The binding of each BamH I subunit is precisely the same as its symmetrical partner. The recognition site for BamH I has a palindromic sequence which can be cut in half for ease in showing bonds.
GC C C T A G
As of the end of 2010, there were 5 crystal structures of BamH I in the Protein Data Bank
BamHI, type II restriction endonucleases, often requires divalent metals as cofactors to catalyze DNA cleavage. Two-metal ion mechanism is one of the possible catalytic mechanisms of BamHI since the BamHI crystal structure has the ability to bind two metal ions at the active site, which is suitable for the classical two-metal ion mechanism to proceed. Two-metal ion mechanism is the use of two metal ions to catalyze the cleavage reaction of restriction enzyme. BamHI has three critical active site residues that are important for metal catalyst. They are known as Asp94, Glu111 and Glu113. These residues are usually acidic. In the presence of a metal ion, the residues are pointed toward the metal ion. In the absence of metal ions, the residues are pointed outward. The two metal ions (A and B) are 4.1 apart from each other in the active site and are in-line with these residues. In general, when the two metal ions (A and B) are bonded to the active site, they help stabilize a cluster distribution of negative charges localized at the active site created by the leaving of an oxygen atom during the transition state. First, a water molecule will be activated by metal ion A at the active site. This water molecule will act as the attacking molecule attacking the BamHI-DNA complex and thus making the complex negative. Later, another water will bound to metal ion B and donate a proton to the leaving group of complex, stabilizing the build-up of negative charge on the leaving oxygen atom.
The function of Ca2+ in the active site of BamHI is known. It is an inhibitor of DNA cleavage, converting BamHI into the pre-reactive state. This revealed the water molecular is the attacking molecule. It donates a proton to the leaving group that is bounded to Ca2+ forming a 90o O-P-O bond angles. If Glu 113 is replaced by lysine, the cleavage is lost since Glu 113 accepts the proton from the attacking water molecule.
- Ninfa, Alexander (2009). Fundamental Laboratory Approaches for Biochemistry and Biotechnology. Wiley. p. 345. ISBN 978-0470087664.
- Viadiu, hector (1998). "The role of metals in catalysis by the restriction endonuclease BamHI". Nature Structural Biology.
- Mordasini, Tiziana (December 18, 2002). "Why do divalent metal ions either promote or inhibit enzymatic reactions? - The case of BamHI restriction endonuclease from combined quantum-classical simulations". The Journal of Biological Chemistry.
- M. Newman, T. Strzelecka, F.D. Dorner, I. Schildkraut, A. K. Aggarwal, Science. 269, 656 (1995)
- Deoxyribonuclease BamHI at the US National Library of Medicine Medical Subject Headings (MeSH)
- 5 crystal structures
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Restriction endonuclease BamHI Provide feedback
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External database links
This tab holds annotation information from the InterPro database.
InterPro entry IPR004194
There are four classes of restriction endonucleases: types I, II,III and IV. All types of enzymes recognise specific short DNA sequences and carry out the endonucleolytic cleavage of DNA to give specific double-stranded fragments with terminal 5'-phosphates. They differ in their recognition sequence, subunit composition, cleavage position, and cofactor requirements [PUBMED:15121719, PUBMED:12665693], as summarised below:
- Type I enzymes (EC) cleave at sites remote from recognition site; require both ATP and S-adenosyl-L-methionine to function; multifunctional protein with both restriction and methylase (EC) activities.
- Type II enzymes (EC) cleave within or at short specific distances from recognition site; most require magnesium; single function (restriction) enzymes independent of methylase.
- Type III enzymes (EC) cleave at sites a short distance from recognition site; require ATP (but doesn't hydrolyse it); S-adenosyl-L-methionine stimulates reaction but is not required; exists as part of a complex with a modification methylase methylase (EC).
- Type IV enzymes target methylated DNA.
Type II restriction endonucleases (EC) are components of prokaryotic DNA restriction-modification mechanisms that protect the organism against invading foreign DNA. These site-specific deoxyribonucleases catalyse the endonucleolytic cleavage of DNA to give specific double-stranded fragments with terminal 5'-phosphates. Of the 3000 restriction endonucleases that have been characterised, most are homodimeric or tetrameric enzymes that cleave target DNA at sequence-specific sites close to the recognition site. For homodimeric enzymes, the recognition site is usually a palindromic sequence 4-8 bp in length. Most enzymes require magnesium ions as a cofactor for catalysis. Although they can vary in their mode of recognition, many restriction endonucleases share a similar structural core comprising four beta-strands and one alpha-helix, as well as a similar mechanism of cleavage, suggesting a common ancestral origin [PUBMED:15770420]. However, there is still considerable diversity amongst restriction endonucleases [PUBMED:14576294, PUBMED:11827971]. The target site recognition process triggers large conformational changes of the enzyme and the target DNA, leading to the activation of the catalytic centres. Like other DNA binding proteins, restriction enzymes are capable of non-specific DNA binding as well, which is the prerequisite for efficient target site location by facilitated diffusion. Non-specific binding usually does not involve interactions with the bases but only with the DNA backbone [PUBMED:11557805].
Below is a listing of the unique domain organisations or architectures in which this domain is found. More...
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This clan includes a large number of nuclease families related to holliday junction resolvases [1,2].
The clan contains the following 127 members:ArenaCapSnatch BamHI BpuJI_N BpuSI_N Bse634I BsuBI_PstI_RE Cas_APE2256 Cas_Cas02710 Cas_Cas4 Cas_Csm6 Cas_DxTHG Cas_NE0113 CoiA Csa1 Dna2 DpnI DpnII DUF1016 DUF1780 DUF1887 DUF2034 DUF2161 DUF234 DUF2357 DUF2726 DUF2800 DUF2887 DUF3799 DUF3883 DUF4143 DUF4263 DUF4420 DUF559 EcoRI EcoRII-C eIF-3_zeta Endonuc-BglII Endonuc-BsobI Endonuc-EcoRV Endonuc-FokI_C Endonuc-HincII Endonuc-MspI Endonuc-PvuII Endonuc_BglI Endonuc_Holl ERCC4 Exo5 Flu_PA Herpes_alk_exo Herpes_UL24 Hjc HSDR_N HSDR_N_2 L_protein_N McrBC MepB MmcB-like Mrr_cat Mrr_cat_2 MutH MvaI_BcnI NaeI NERD NgoMIV_restric NotI NucS PDCD9 PDDEXK_1 PDDEXK_10 PDDEXK_2 PDDEXK_3 PDDEXK_4 PDDEXK_5 PDDEXK_7 PDDEXK_9 Pet127 Phage_endo_I R-HINP1I Rad10 RAI1 RAP RE_AlwI RE_ApaLI RE_Bpu10I RE_Bsp6I RE_CfrBI RE_Eco47II RE_EcoO109I RE_HaeII RE_HindIII RE_HindVP RE_HpaII RE_LlaJI RE_LlaMI RE_MjaI RE_NgoBV RE_NgoPII RE_SacI RE_ScaI RE_SinI RE_TaqI RE_TdeIII RE_XamI RE_XcyI RecU RestrictionMunI RestrictionSfiI RmuC RNA_pol_Rpb5_N Sen15 SfsA Spo0A_C TBPIP_N ThaI Tn7_Tnp_TnsA_N Transposase_31 tRNA_int_endo Tsp45I Uma2 UPF0102 VirArc_Nuclease VRR_NUC Vsr XhoI XisH YaeQ YqaJ
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1Cannot generate PP/Heatmap alignments for seeds; no PP data available
Key: available, not generated, — not available.
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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.
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|Seed source:||Structural domain|
|Number in seed:||4|
|Number in full:||22|
|Average length of the domain:||136.10 aa|
|Average identity of full alignment:||51 %|
|Average coverage of the sequence by the domain:||76.68 %|
|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:||14|
|Download:||download the raw HMM for this family|
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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.
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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.
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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.
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There is 1 interaction 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 BamHI domain has been found. There are 9 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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