Summary: Single-strand binding protein family
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This is the Wikipedia entry entitled "Single-stranded binding protein". More...
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Single-stranded binding protein Edit Wikipedia article
Crystal structure of PriB- a primosomal DNA replication protein of Escherichia coli
Single-stranded binding proteins (SSBPs) are a class of proteins that have been identified in both viruses and organisms from bacteria to humans.
Single stranded binding proteins prevent premature annealing (binding of complementary DNA sequences), protect the single-stranded DNA from being digested by nucleases, and prevent secondary structure formation, thereby allowing other enzymes to function effectively on the single strand.
Single stranded DNA-binding protein(icp8) from herpes simplex virus-1
In ICP8, the herpes simplex virus (HSV-1) single-strand DNA-binding protein (ssDNA-binding protein (SSB)), The head consists of the eight alpha helices. The front side of the neck region consists of a five-stranded beta-sheet and two alpha helices, whereas the back side is a three-stranded beta-sheet The shoulder part of the N-terminal domain contains an alpha-helical and beta-sheet region. The herpes simplex virus (HSV-1) SSB, ICP8, is a nuclear protein that, along other replication proteins is required for viral DNA replication during lytic infection.
Six herpes virus-group-common genes encode proteins that likely constitute the replication fork machinery, including a two-subunit DNA polymerase, a Helicase-primase complex and a single-stranded DNA-binding protein. The human herpesvirus 1 (HHV-1) single-strand DNA-binding protein ICP8 is a 128kDa zinc metalloprotein. Photoaffinity labeling has shown that the region encompassing amino acid residues 368-902 contains the single-strand DNA-binding site of ICP8. The HHHV-1 UL5, UL8, and UL52 genes encode an essential heterotrimeric DNA helicase-primase that is responsible for concomitant DNA unwinding and primer synthesis at the viral DNA replication fork. ICP8 may stimulate DNA unwinding and enable bypass of cisplatin damaged DNA by recruiting the helicase-primase to the DNA.
In molecular biology, SSB protein domains in bacteria are important maintaining DNA metabolism, more specifically DNA replication, repair and recombination. It has a structure of three beta-strands to a single six-stranded beta-sheet to form a dimer.
Eukaryotic replication protein A
Replication protein A(heterotrimer)
|This is an image of human Replication protein A. From Proteopedia protein A Replication protein A|
|Replication protein A1||RPA1||Chr. 17 p13.3|
|Replication protein A2||RPA2||Chr. 1 p35.3|
|Replication protein A3||RPA3||Chr. 7 p21.3|
Replication protein A is the functional equivalent of SSB in the nucleus of eukaryotic cells, though there is no sequence homology.
Eukaryotic mitochondrial SSB
The mitochondria of eukaryotic cells contain their own single stranded DNA binding protein. Human mitochondrial SSB (mtSSB) binds to single-stranded mitochondrial DNA as a tetramer and has sequence similarity to bacterial SSB. Human mtSSB is encoded by the SSBP1 gene. In yeast, it is encoded by the RIM1 gene.
- Mapelli M, Panjikar S, Tucker PA (2005). "The crystal structure of the herpes simplex virus 1 ssDNA-binding protein suggests the structural basis for flexible, cooperative single-stranded DNA binding". J Biol Chem. 280 (4): 2990–7. doi:10.1074/jbc.M406780200. PMID 15507432.
- Anders DG, McCue LA (1996). "The human cytomegalovirus genes and proteins required for DNA synthesis". Intervirology. 39 (5-6): 378–88. PMID 9130047.
- White EJ, Boehmer PE (October 1999). "Photoaffinity labeling of the herpes simplex virus type-1 single-strand DNA-binding protein (ICP8) with oligodeoxyribonucleotides". Biochem. Biophys. Res. Commun. 264 (2): 493–7. doi:10.1006/bbrc.1999.1566. PMID 10529391.
- Tanguy Le Gac N, Villani G, Boehmer PE (May 1998). "Herpes simplex virus type-1 single-strand DNA-binding protein (ICP8) enhances the ability of the viral DNA helicase-primase to unwind cisplatin-modified DNA". J. Biol. Chem. 273 (22): 13801–7. doi:10.1074/jbc.273.22.13801. PMID 9593724.
- Meyer RR, Laine PS (December 1990). "The single-stranded DNA-binding protein of Escherichia coli". Microbiol. Rev. 54 (4): 342–80. PMC . PMID 2087220.
- Raghunathan S, Ricard CS, Lohman TM, Waksman G (June 1997). "Crystal structure of the homo-tetrameric DNA binding domain of Escherichia coli single-stranded DNA-binding protein determined by multiwavelength x-ray diffraction on the selenomethionyl protein at 2.9-A resolution". Proc. Natl. Acad. Sci. U.S.A. 94 (13): 6652–7. doi:10.1073/pnas.94.13.6652. PMC . PMID 9192620.
- Tiranti, V; Rocchi, M; DiDonato, S; Zeviani, M (30 April 1993). "Cloning of human and rat cDNAs encoding the mitochondrial single-stranded DNA-binding protein (SSB).". Gene. 126 (2): 219–25. PMID 8482537.
- Van Dyck, E; Foury, F; Stillman, B; Brill, SJ (September 1992). "A single-stranded DNA binding protein required for mitochondrial DNA replication in S. cerevisiae is homologous to E. coli SSB.". The EMBO journal. 11 (9): 3421–30. PMID 1324172.
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.
Single-strand binding protein family Provide feedback
This family includes single stranded binding proteins and also the primosomal replication protein N (PriB). PriB forms a complex with PriA, PriC and ssDNA.
Raghunathan S, Ricard CS, Lohman TM, Waksman G; , Proc Natl Acad Sci U S A 1997;94:6652-6657.: Crystal structure of the homo-tetrameric DNA binding domain of Escherichia coli single-stranded DNA-binding protein determined by multiwavelength x-ray diffraction on the selenomethionyl protein at 2.9-A resolution. PUBMED:9192620 EPMC:9192620
Webster G, Genschel J, Curth U, Urbanke C, Kang C, Hilgenfeld R; , FEBS Lett 1997;411:313-316.: A common core for binding single-stranded DNA: structural comparison of the single-stranded DNA-binding proteins (SSB) from E. coli and human mitochondria. PUBMED:9271227 EPMC:9271227
Internal database links
|Similarity to PfamA using HHSearch:||tRNA_anti-codon|
External database links
This tab holds annotation information from the InterPro database.
InterPro entry IPR000424
The Escherichia coli single-strand binding protein [PUBMED:2087220] (gene ssb), also known as the helix-destabilising protein, is a protein of 177 amino acids. It binds tightly, as a homotetramer, to single-stranded DNA (ss-DNA) and plays an important role in DNA replication, recombination and repair. Closely related variants of SSB are encoded in the genome of a variety of large self-transmissible plasmids. SSB has also been characterised in bacteria such as Proteus mirabilis or Serratia marcescens. Eukaryotic mitochondrial proteins that bind ss-DNA and are probably involved in mitochondrial DNA replication are structurally and evolutionary related to prokaryotic SSB.
The mapping between Pfam and Gene Ontology is provided by InterPro. If you use this data please cite InterPro.
|Molecular function||single-stranded DNA binding (GO:0003697)|
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
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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.
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The OB (oligonucleotide/oligosaccharide binding) was defined by Murzin . The common part of the OB-fold, has a five-stranded beta-sheet coiled to form a closed beta-barrel. This barrel is capped by an alpha-helix located between the third and fourth strands .
The clan contains the following 70 members:BOF BRCA-2_OB1 BRCA-2_OB3 CDC24_OB1 CDC24_OB2 CDC24_OB3 CSD CusF_Ec DNA_ligase_A_C DNA_ligase_OB DNA_ligase_OB_2 DUF1344 DUF2110 DUF223 DUF3127 DUF4539 EFP eIF-1a eIF-5a Elong-fact-P_C EutN_CcmL EXOSC1 MCM_OB mRNA_cap_C MRP-S35 NigD_N NlpE_C OB_aCoA_assoc OB_NTP_bind OB_RNB PCB_OB Phage_DNA_bind POT1 Prot_ATP_ID_OB RecG_wedge RecO_N RecO_N_2 Rep-A_N Rep_fac-A_3 Rep_fac-A_C REPA_OB_2 Rho_RNA_bind Ribosom_S12_S23 Ribosomal_L2 Ribosomal_S17 Ribosomal_S28e RMI2 RNA_pol_Rbc25 RNA_pol_Rpb8 RNA_pol_RpbG Rrp44_CSD1 Rrp44_S1 RsgA_N RuvA_N S1 S1-like S1_2 SSB Stn1 TEBP_beta Ten1 Ten1_2 TOBE TOBE_2 TOBE_3 TRAM tRNA_anti-codon tRNA_anti-like tRNA_anti_2 tRNA_bind
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:
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You can download (or view in your browser) a text representation of a Pfam alignment in various formats:
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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...
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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.
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.
|Seed source:||Prosite & COG2965|
|Author:||Finn RD, Bateman A|
|Number in seed:||52|
|Number in full:||8735|
|Average length of the domain:||102.70 aa|
|Average identity of full alignment:||28 %|
|Average coverage of the sequence by the domain:||63.87 %|
|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:||24|
|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.
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
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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 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 SSB domain has been found. There are 129 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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