Summary: SCA7, zinc-binding domain
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SCA7, zinc-binding domain Provide feedback
This domain is found in the protein Sgf73/Sca7 which is a component of the multihistone acetyltransferase complexes SAGA and SILK . This domain is also found in Ataxin-7, a human protein which in its polyglutamine expanded pathological form, is responsible for the neurodegenerative disease spinocerebellar ataxia 7 (SCA7) . Ataxin-7 is an integral component of the mammalian SAGA-like complexes, the TATA-binding protein-free TAF-containing complex (TFTC) and the SPT3/TAF9/GCN5 acetyltransferase complex (STAGA). This domain is a minimal domain in ataxin-7-like proteins that is required for interaction with TFTC/STAGA subunits and is conserved highly through evolution. The domain contains a conserved Cys(3)His motif that binds zinc, thus indicating this to be a new zinc-binding domain .
McMahon SJ, Pray-Grant MG, Schieltz D, Yates JR 3rd, Grant PA; , Proc Natl Acad Sci U S A 2005;102:8478-8482.: Polyglutamine-expanded spinocerebellar ataxia-7 protein disrupts normal SAGA and SLIK histone acetyltransferase activity. PUBMED:15932941 EPMC:15932941
Helmlinger D, Hardy S, Sasorith S, Klein F, Robert F, Weber C, Miguet L, Potier N, Van-Dorsselaer A, Wurtz JM, Mandel JL, Tora L, Devys D;, Hum Mol Genet. 2004;13:1257-1265.: Ataxin-7 is a subunit of GCN5 histone acetyltransferase-containing complexes. PUBMED:15115762 EPMC:15115762
This tab holds annotation information from the InterPro database.
InterPro entry IPR013243
SAGA (Spt-Ada-Gcn5 acetyltransferase), a coactivator complex involved in chromatin remodelling, harbours both histone acetylation and deubiquitination activities. SAGA-associated factor 73 (Sgf734/ATXN7) and Ataxin-7-like protein 3 (ATXN7L3), two subunits of the SAGA deubiquitination module, contain an ~50-residue SCA7 domain characterised by an atypical zinc- finger (Znf) with a Cys-X(9,10)-Cys-X(5)-Cys-X(2)-His motif and a long sequence insertion between the first two zinc coordinating residues.
The SCA7 domain is found exclusively in members of the ATXN7 gene family, which includes two distinct subunits of SAGA complexes: ATXN7 and ATXN7L3 orthologues. The analysis of multiple alignments highlights the consensus signature for the SCA7 domain, encompassing the putative zinc- coordinating residues, but also reveals the distinct features of the two proteins. Marked differences are found mostly in the carboxy-terminal of the domain, suggesting that divergent evolution of the SCA7 Znf domain occurred in order to achieve specific functions in the SAGA complex. Both SCA7 domains contain disordered regions, albeit not in the same region. Whereas the first and last 10 residues of ATXN7-SCA7 are not folded, the N- terminal region of ATXN7L3-SCA7 is well structured and the last 30 residues of this domain are not folded. In both ATXN7-SCA7 and ATXN7L3-SCA7, the large sequence insertion between the first and second zinc- coordinating cysteines corresponds to a protruding extended hairpin structure. The core of the zinc-binding sites shows a conserved structure formed by two short adjacent loops located at the bottom of the hairpin. Although the SCA7 domains of both ATXN7 and ATXN7L3 contain two alpha-helices, these are not located at similar positions in the sequences. In ATXN7-SCA7, the two alpha- helices are located downstream from the zinc-binding site and are separated by a loop containing a large number of positively charged residues. In ATXN7L3- SCA7, the two helices lie to either side of the zinc-binding site, leading to a different packing of the two helices. In ATXN7-SCA7, the two helices have an almost perpendicular orientation, the alpha2 helix being anchored to the zinc- binding site. In ATXN7L3-SCA7, the helices alpha1 and alpha2 adopt an anti- parallel orientation defined by hydrophobic interactions. The ATXN7-SCA7 domain binds to the core or the C-terminal ends of the histone H2A and H2B dimer, a region located on the lateral face of the nucleosome that contains the ubiquitinated Lys 120 of H2B. This property is lost in the ATXN7-SCA7 domain [PUBMED:15932941, PUBMED:20634802].
This entry represents the SCA7 domain.
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:
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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:||Pfam-B_21229 (release 17.0)|
|Author:||Mistry J, Wood V|
|Number in seed:||42|
|Number in full:||857|
|Average length of the domain:||65.70 aa|
|Average identity of full alignment:||44 %|
|Average coverage of the sequence by the domain:||11.69 %|
|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:||11|
|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.
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 SCA7 domain has been found. There are 2 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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