Summary: Bacterial DNA-binding protein
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Bacterial DNA binding protein Edit Wikipedia article
anabaena hu-dna cocrystal structure (ahu6)
In molecular biology, bacterial DNA binding proteins are a family of small, usually basic proteins of about 90 residues that bind DNA and are known as histone-like proteins. Since bacterial binding proteins have a diversity of functions, it has been difficult to develop a common function for all of them. They are commonly referred to as histone-like and have many similar traits with the eukaryotic histone proteins. Eukaryotic histones package DNA to help it to fit in the nucleus, and they are known to be the most conserved proteins in nature. Examples include the HU protein in Escherichia coli, a dimer of closely related alpha and beta chains and in other bacteria can be a dimer of identical chains. HU-type proteins have been found in a variety of eubacteria, cyanobacteria and archaebacteria, and are also encoded in the chloroplast genome of some algae. The integration host factor (IHF), a dimer of closely related chains which is suggested to function in genetic recombination as well as in translational and transcriptional control is found in Enterobacteria and viral proteins including the African swine fever virus protein A104R (or LMW5-AR).
Histone-like proteins are present in many Eubacteria, Cyanobacteria, and Archaebacteria. These proteins participate in all DNA-dependent functions; in these processes, bacterial DNA binding proteins have an architectural role, maintaining structural integrity as transcription, recombination, replication, or any other DNA-dependent process proceeds. Eukaryotic histones were first discovered through experiments in 0.4M NaCl. In these high salt concentrations, the eukaryotic histone protein is eluted from a DNA solution in which single stranded DNA is bound covalently to cellulose. Following elution, the protein readily binds DNA, indicating the protein's high affinity for DNA. Histone-like proteins were unknown to be present in bacteria until similarities between eukaryotic histones and the HU-protein were noted, particularly because of the abundancy, basicity, and small size of both of the proteins. Upon further investigation, it was discovered that the amino acid composition of HU resembles that of eukaryotic histones, thus prompting further research into the exact function of bacterial DNA binding proteins and discoveries of other related proteins in bacteria.
Role in DNA replication
Research suggests that bacterial DNA binding protein has an important role during DNA replication; the protein is involved in stabilizing the lagging strand as well as interacting with DNA polymerase III. The role of single-stranded DNA binding (SSB) protein during DNA replication in Escherichia coli cells has been studied, specifically the interactions between SSB and the χ subunit of DNA polymerase III in environments of varying salt concentrations.
In DNA replication at the lagging strand site, DNA polymerase III removes nucleotides individually from the DNA binding protein. An unstable SSB/DNA system would result in rapid disintegration of the SSB, which stalls DNA replication. Research has shown that the ssDNA is stabilized by the interaction of SSB and the χ subunit of DNA polymerase III in E. coli, thus preparing for replication by maintaining the correct conformation that increases the binding affinity of enzymes to ssDNA. Furthermore, binding of SSB to DNA polymerase III at the replication fork prevents dissociation of SSB, consequently increasing the efficiency of DNA polymerase III to synthesize a new DNA strand.
Initially, bacterial DNA binding proteins were thought to help stabilize bacterial DNA. Currently, many more functions of bacteria DNA binding proteins have been discovered, including the regulation of gene expression by histone-like nucleoid-structuring protein, H-NS.
H-NS is about 15.6 kDa and assists in the regulation of bacterial transcription in bacteria by repressing and activating certain genes. H-NS binds to DNA with an intrinsic curvature. In E. coli, H-NS binds to a P1 promoter decreasing rRNA production during stationary and slow growth periods. RNA polymerase and H-NS DNA binding protein have overlapping binding sites; it is thought that H-NS regulates rRNA production by acting on the transcription initiation site. It has been found that H-NS and RNA polymerase both bind to the P1 promoter and form a complex. When H-NS is bound with RNA Polymerase to the promoter region, there are structural differences in the DNA that are accessible. It has also been found that H-NS can affect translation as well by binding to mRNA and causing its degradation.
HU is a small (10 kDa) bacterial histone-like protein that resembles the eukaryotic Histone H2B. HU acts similarly to a histone by inducing negative supercoiling into circular DNA with the assistance of topoisomerase. The protein has been implicated in DNA replication, recombination, and repair. With an α-helical hydrophobic core and two positively charged β-ribbon arms, HU binds non-specifically to dsDNA with low affinity but binds to altered DNA—such as junctions, nicks, gaps, forks, and overhangs—with high affinity. The arms bind to the minor groove of DNA in low affinity states; in high affinity states, a component of the α-helical core interacts with the DNA as well. However, this protein’s function is not solely confined to DNA; HU also binds to RNA and DNA-RNA hybrids with the same affinity as supercoiled DNA.
Recent research has revealed that HU binds with high specificity to the mRNA of rpoS, a transcript for the stress sigma factor of RNA polymerase, and stimulates translation of the protein. Additional to this RNA function, it was also demonstrated that HU binds DsrA, a small non-coding RNA that regulates transcription through repressing H-NS and stimulates translation through increasing expression of rpoS. These interactions suggest that HU has multiple influences on transcription and translation in bacterial cells.
Integration host factor, IHF, is a nucleoid-associated protein only found in gram negative bacteria. It is a 20 kDa heterodimer, composed of α and β subunits that bind to the sequence 5' - WATCAANNNNTTR - 3' and bends the DNA approximately 160 degrees. The β arms of IHF have Proline residues that help stabilize the DNA kinks. These kinks can help compact DNA and allow for supercoiling. The mode of binding to DNA depends on environmental factors, such as the concentration of ions present. With a high concentration of KCl, there is weak DNA bending. It has been found that sharper DNA bending occurs when the concentration of KCl is less than 100 mM, and IHF is not concentrated.
IHF was discovered as a necessary co-factor for recombination of λ phage in to E.coli. In 2016 it was discovered that IHF also plays a key role in CRISPR type I and type II systems. It has a major role in allowing the Cas1-Cas2 complex to integrate new spacers into the CRISPR sequence. The bending of the DNA by IHF is thought to alter spacing in the DNA major and minor grooves, allowing the Cas1-Cas2 complex to make contact with the DNA bases. This is a key function in the CRISPR system as it ensures that new spacers area always added at the beginning of the CRISPE sequence next to the leader sequence. This directing of integration by IHF ensures that spacers are added chronologically, allowing better protection against the most recent viral infection.
|DNA Binding Protein||Size||Structure||Binding Site||Effect|
|H-NS||15.6 kDa||exists in dimers to physically prevent RNA polymerase from binding to promoter||binds to bent DNA, binds to P1 promoter in E. coli||regulation of gene expression|
|HU||10 kDa||α-helical core and two positively charged β-ribbon arms||binds non-specifically to dsDNA, binds to DsrA, a small non-coding RNA that regulates transcription||induces negative supercoiling into circular DNA|
|IHF||20 kDa||αβαβ hetrodimer||binds to specific sequences of DNA||creates kinks in DNA|
Implications and further research
The functions of bacterial DNA-binding proteins are not limited to DNA replication. Researchers have been investigating other pathways these proteins affect. The DNA-binding protein H-NS has been known to play roles in chromosome organization and gene regulation; however, recent studies have also confirmed their role in indirectly regulating flagella functions. Some motility regulatory linkages that H-NS influences include the messenger molecule Cyclic di-GMP, the bio-film regulatory protein CsgD, and the sigma factors, σ(S) and σ(F). Further studies are aiming to characterize the ways this nucleoid-organizing protein affects the motility of the cell through other regulatory pathways.
Other researchers have used bacterial DNA-binding proteins to research Salmonella enterica serovar Typhimurium, in which the T6SS genes are activated from a macrophage infection. When S. Typhimurium infects, their efficiency can be improved through a sense-and-kill mechanism with T6SS H-NS silencing. Assays are created that combine reporter fusions, electrophoretic mobility shift assays, DNase footprinting, and fluorescence microscopy to silence the T6SS gene cluster by the histone-like nucleoid structuring H-NS protein.
- Drlica K, Rouviere-Yaniv J (September 1987). "Histonelike proteins of bacteria". Microbiol. Rev. 51 (3): 301–19. PMC . PMID 3118156.
- Pettijohn DE (September 1988). "Histone-like proteins and bacterial chromosome structure". J. Biol. Chem. 263 (26): 12793–6. PMID 3047111.
- Griffiths, Anthony; Wessler, Susan; Carroll, Sean; Doebly, John. Introduction to Genetic Analysis (10 ed.). New York: W. H. Freeman and Company. pp. 428–429.
- Wang SL, Liu XQ (December 1991). "The plastid genome of Cryptomonas phi encodes an hsp70-like protein, a histone-like protein, and an acyl carrier protein". Proc. Natl. Acad. Sci. U.S.A. 88 (23): 10783–7. PMC . PMID 1961745. doi:10.1073/pnas.88.23.10783.
- Friedman DI (November 1988). "Integration host factor: a protein for all reasons". Cell. 55 (4): 545–54. PMID 2972385. doi:10.1016/0092-8674(88)90213-9.
- Neilan JG, Lu Z, Kutish GF, Sussman MD, Roberts PC, Yozawa T, Rock DL (March 1993). "An African swine fever virus gene with similarity to bacterial DNA binding proteins, bacterial integration host factors, and the Bacillus phage SPO1 transcription factor, TF1". Nucleic Acids Res. 21 (6): 1496. PMC . PMID 8464748. doi:10.1093/nar/21.6.1496.
- Drlica, Karl; Rouviere-Yaniv, Josette (September 1987). "Histonelike Proteins of Bacteria". Microbiological Reviews. 51 (3): 301–319. PMC . PMID 3118156.
- Witte, Gregor; Urbanke, Claus; Curth, Ute (June 5, 2003). "DNA polymerase III χ subunit ties single-stranded DNA binding protein to the bacterial replication machinery". Nucleic Acids Research. 31 (15): 4434–4440. PMC . PMID 12888503. doi:10.1093/nar/gkg498.
- Dorman, Charles J; Deighan, Padraig (2003-04-01). "Regulation of gene expression by histone-like proteins in bacteria". Current Opinion in Genetics & Development. 13 (2): 179–184. doi:10.1016/S0959-437X(03)00025-X.
- Schroder, Oliver; Wagner, Rolf (May 19, 2000). "The bacterial DNA-binding protein H-NS represses ribosomal RNA transcription by tapping RNA polymerase in the initiation complex". Journal of Molecular Biology. 298 (5): 737–748. PMID 10801345. doi:10.1006/jmbi.2000.3708.
- Serban, D.; Arcineigas, S. F.; Vorgias, C. E.; Thomas, G. J. (2003). "Structure and dynamics of the DNA-binding protein HU of B. stearothermophilus investigated by Raman and ultraviolet-resonance Raman spectroscopy". Protein Science. 12 (4): 861–870. PMC . PMID 12649443. doi:10.1110/ps.0234103.
- Balandina, Anna; Kamashev, Dmitri; Rouviere-Yaniv, Josette (August 2, 2002). "The bacterial histone-like protein HU specifically recognizes similar structures in all nucleic acids". The Journal of Biological Chemistry. 277 (31): 27622. PMID 12006568. doi:10.1074/jbc.M201978200. Retrieved 15 October 2015.
- Balandina, Anna, et al. "The Escherichia coli histone‐like protein HU regulates rpoS translation." Molecular microbiology 39.4 (2001): 1069-1079.
- Dillon, Shane C.; Dorman, Charles J. (2010-03-01). "Bacterial nucleoid-associated proteins, nucleoid structure and gene expression". Nature Reviews Microbiology. 8 (3): 185–195. ISSN 1740-1526. doi:10.1038/nrmicro2261.
- Nuñez, James K.; Bai, Lawrence; Harrington, Lucas B.; Hinder, Tracey L.; Doudna, Jennifer A. (2016-06-16). "CRISPR Immunological Memory Requires a Host Factor for Specificity". Molecular Cell. 62 (6): 824–833. ISSN 1097-4164. PMID 27211867. doi:10.1016/j.molcel.2016.04.027.
- Lin, J.; Chen, H.; Droge, P.; Yan, J. (2012). "Physical Organization of DNA by Multiple Non-Specific DNA-Binding Modes of Integration Host Factor (IHF)". PLoS ONE. 7 (11): e49885. PMC . PMID 23166787. doi:10.1371/journal.pone.0049885.
- Nuñez, James K.; Bai, Lawrence; Harrington, Lucas B.; Hinder, Tracey L.; Doudna, Jennifer A. (2016-06-16). "CRISPR Immunological Memory Requires a Host Factor for Specificity". Molecular Cell. 62 (6): 824–833. ISSN 1097-4164. PMID 27211867. doi:10.1016/j.molcel.2016.04.027.
- Sorek, Rotem; Lawrence, C. Martin; Wiedenheft, Blake (2013). "CRISPR-Mediated Adaptive Immune Systems in Bacteria and Archaea". Annual Review of Biochemistry. 82 (1): 237–266. doi:10.1146/annurev-biochem-072911-172315.
- Kim, EA; Blair, DF (20 July 2015). "Function of the Histone-Like Protein H-NS in Motility of Escherichia coli: Multiple Regulatory Roles Rather than Direct Action at the Flagellar Motor". Journal of Bacteriology. 197 (19): 3110–20. PMC . PMID 26195595. doi:10.1128/JB.00309-15.
- Brunet, Yannick R.; Khodr, Ahmad; Logger, Laureen; Aussel, Laurent; Mignot, Tâm; Rimsky, Sylvie; Cascales, Eric (2015-07-01). "H-NS Silencing of the Salmonella Pathogenicity Island 6-Encoded Type VI Secretion System Limits Salmonella enterica Serovar Typhimurium Interbacterial Killing". Infection and Immunity. 83 (7): 2738–2750. ISSN 1098-5522. PMC . PMID 25916986. doi:10.1128/IAI.00198-15.
This tab holds the annotation information that is stored in the Pfam database. As we move to using Wikipedia as our main source of annotation, the contents of this tab will be gradually replaced by the Wikipedia tab.
Bacterial DNA-binding protein Provide feedback
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Internal database links
|SCOOP:||DUF2267 DUF4496 HU-DNA_bdg|
|Similarity to PfamA using HHSearch:||HU-DNA_bdg DUF4496|
External database links
This tab holds annotation information from the InterPro database.
InterPro entry IPR000119
Bacteria synthesise a set of small, usually basic proteins of about 90 residues that bind DNA and are known as histone-like proteins [PUBMED:3118156, PUBMED:3047111]. Examples include the HU protein in Escherichia coli is a dimer of closely related alpha and beta chains and in other bacteria can be a dimer of identical chains. HU-type proteins have been found in a variety of eubacteria, cyanobacteria and archaebacteria, and are also encoded in the chloroplast genome of some algae [PUBMED:1961745]. The integration host factor (IHF), a dimer of closely related chains which seem to function in genetic recombination as well as in translational and transcriptional control [PUBMED:2972385] is found in enterobacteria and viral proteins include the African Swine fever virus protein A104R (or LMW5-AR) [PUBMED:8464748].
The exact function of these proteins is not yet clear but they are capable of wrapping DNA and stabilising it from denaturation under extreme environmental conditions. The structure is known for one of these proteins [PUBMED:6540370]. The protein exists as a dimer and two "beta-arms" function as the non-specific binding site for bacterial DNA.
The mapping between Pfam and Gene Ontology is provided by InterPro. If you use this data please cite InterPro.
|Molecular function||DNA binding (GO:0003677)|
Below is a listing of the unique domain organisations or architectures in which this domain is found. More...
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This superfamily is characterised by being a dimer of identical subunits of a core of four helices in a bundle, partly opened, capped with a beta-sheet. All members appear to be prokaryotic DNA-binding domains.
The clan contains the following 3 members:Bac_DNA_binding HU-DNA_bdg Tra_M
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...
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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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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:||116|
|Number in full:||10404|
|Average length of the domain:||89.40 aa|
|Average identity of full alignment:||34 %|
|Average coverage of the sequence by the domain:||82.61 %|
|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:||20|
|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.
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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:
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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 Bac_DNA_binding domain has been found. There are 73 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 sequence.
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