Summary: Signal peptidase, peptidase S26

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Wikipedia: Signal peptidase
Pfam
InterPro

This is the Wikipedia entry entitled "Signal peptidase". More...

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Signal peptidase Edit Wikipedia article

Initially observed in preparations of Endoplasmci reticulum (ER)-derived membranes, so called "microsomes" from mouse myeloma cells ^[1], 'signal peptidase convert secretory and some membrane proteins to their mature form. The key observation by Milstein et al. was that immunoglobulin light chains were produced in a higher molecular weight form, which became processed by the microsomal fraction. This finding was directly followed by the discovery of the ER translocation machinery ^[2]. Signal peptidases are also found in prokaryotes as well as the protein import machinery of mitochondria and chloroplasts ^[3].

All signal peptidases described so far are serine proteases. The active site that endoproteolytically cleaves signal peptides from translocated precursor proteins is located at the extracytoplasmic site of the membrane. The eukaryotic signal peptidase is an integral membrane protein complex. The first subunit, which was identified genetically, is Sec11, yeast membrane protein of 17 kDa. Sec11 is associated with three subunits termed Spc3p (21 kDa), Spc2p (18 kDa) and Spc1p (11 kDa). Sec11 is the only essential factor for signal peptide processing as can be deduced from a growth defect upon its deletion ^[4]. The functional signal peptidase complex was first purified from canine microsomes ^[5]. The five mammalian subunits are named SPC12, SPC18, SPC21, SPC22/23 and SPC25 according to their molecular weight.

^ Milstein, C., Brownlee, G. G., Harrison, T. M., and Mathews, M. B. (1972). A possible precursor of immunoglobulin light chains. Nat New Biol 239, PP. 117-120
^ Blobel, G., and Dobberstein, B. (1975). Transfer of proteins across membranes. I. Presence of proteolytically processed and unprocessed nascent immunoglobulin light chains on membrane-bound ribosomes of murine myeloma. J Cell Biol 67, PP. 835-851
^ Paetzel, M., Karla, A., Strynadka, N. C., and Dalbey, R. E. (2002b). Signal peptidases. Chem Rev 102, PP. 4549-4580
^ Bohni, P. C., Deshaies, R. J., and Schekman, R. W. (1988). SEC11 is required for signal peptide processing and yeast cell growth. J Cell Biol 106, PP. 1035-1042
^ Evans, E. A., Gilmore, R., and Blobel, G. (1986). Purification of microsomal signal peptidase as a complex. Proc Natl Acad Sci U S A 83, PP. 581-585

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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.

Signal peptidase, peptidase S26 Provide feedback

This is a family of membrane signal serine endopeptidases which function in the processing of newly-synthesised secreted proteins. Peptidase S26 removes the hydrophobic, N-terminal, signal peptides as proteins are translocated across membranes. The active site residues take the form of a catalytic dyad that is Ser, Lys in subfamily S26A; the Ser is the nucleophile in catalysis, and the Lys is the general base.

Internal database links

SCOOP:	Peptidase_S24
Similarity to PfamA using HHSearch:	Peptidase_S24

External database links

MEROPS:

S26

This tab holds annotation information from the InterPro database.

InterPro entry IPR019533

This entry represents a domain found in some members of the S26A family of serine endopeptidases. Peptidases S26A (signal peptidase I) removes the hydrophobic, N-terminal signal peptides as proteins are translocated across membranes. The type I signal peptidases are unique serine proteases that utilize a serine/lysine catalytic dyad mechanism in place of the classical serine/histidine/aspartic acid catalytic triad mechanism [ PUBMED:15546672 ]. Peptidases S26B includes eukaryotic microsomal signal peptidases involved in the removal of signal peptides from secretory proteins as they pass into the endoplasmic reticulum lumen [ PUBMED:7845208 ]. Peptidases 26C (TraF signal peptidase) are found in operons that encode elements of conjugative transfer systems.

Gene Ontology

The mapping between Pfam and Gene Ontology is provided by InterPro. If you use this data please cite InterPro.

Molecular function	serine-type endopeptidase activity (GO:0004252)
Biological process	signal peptide processing (GO:0006465)

Domain organisation

Below is a listing of the unique domain organisations or architectures in which this domain is found. More...

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Pfam Clan

This family is a member of clan Peptidase_SF (CL0299), which has the following description:

This clan includes the peptidase S24 and S26 families. These families adopt a mainly beta fold. Members of the family S24 have an additional C-terminal domain containing a bundle of three helices presumably important for binding DNA.

The clan contains the following 3 members:

Peptidase_S24 Peptidase_S26 Phage_CI_C

Alignments

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 and the UniProtKB 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.

Alignment types

We make a range of alignments for each Pfam-A family:

seed: the curated alignment from which the HMM for the family is built
full: the alignment generated by searching the sequence database using the HMM
RP15/RP35/RP55/RP75: Representative Proteomes (RPs) at 15%, 35%, 55% and 75% co-membership thresholds
UniProt: alignment generated by searching the UniProtKB sequence database using the family HMM

Viewing

You can see the alignments as HTML or in three different sequence viewers:

jalview: a Java applet developed at the University of Dundee. You will need Java installed before running jalview
HTML: 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
PP/Heatmap: 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.

Reformatting

You can download (or view in your browser) a text representation of a Pfam alignment in various formats:

Selex
Stockholm
FASTA
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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.

Downloading

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.

View options

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.

	Seed (71)	Full (23661)	Representative proteomes				UniProt (95907)
	Seed (71)	Full (23661)	RP15 (3463)	RP35 (11578)	RP55 (23213)	RP75 (38157)	UniProt (95907)
Jalview	View	View	View	View	View	View	View
HTML	View
PP/heatmap	₁

¹Cannot generate PP/Heatmap alignments for seeds; no PP data available

Key: available, not generated, — not available.

Format an alignment

	Seed (71)	Full (23661)	Representative proteomes				UniProt (95907)
	Seed (71)	Full (23661)	RP15 (3463)	RP35 (11578)	RP55 (23213)	RP75 (38157)	UniProt (95907)
Alignment:
Format:
Order:	Tree Alphabetical
Sequence:	Inserts lower case All upper case
Gaps:
Download/view:	Download View

Download options

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.

	Seed (71)	Full (23661)	Representative proteomes				UniProt (95907)
	Seed (71)	Full (23661)	RP15 (3463)	RP35 (11578)	RP55 (23213)	RP75 (38157)	UniProt (95907)
Raw Stockholm	Download	Download	Download	Download	Download	Download	Download
Gzipped	Download	Download	Download	Download	Download	Download	Download

You can also download a FASTA format file containing the full-length sequences for all sequences in the full alignment.

HMM logo

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...

Trees

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.

Curation

Seed source:

Manual

Previous IDs:

none

Type:

Domain

Sequence Ontology:

SO:0000417

Author:

Mistry J

, Rawlings ND

Number in seed:

71

Number in full:

23661

Average length of the domain:

152.6 aa

Average identity of full alignment:

23 %

Average coverage of the sequence by the domain:

71.63 %

HMM information

HMM build commands:

build method: hmmbuild -o /dev/null HMM SEED

search method: hmmsearch -Z 61295632 -E 1000 --cpu 4 HMM pfamseq

Model details:

Parameter	Sequence	Domain
Gathering cut-off	22.9	22.9
Trusted cut-off	22.9	22.9
Noise cut-off	22.8	22.8

Model length:

170

Family (HMM) version:

12

Download:

download the raw HMM for this family

Species distribution

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Colour assignments

Archea	Eukaryota
Bacteria	Other sequences
Viruses	Unclassified
Viroids	Unclassified sequence

Selections

Align selected sequences to HMM

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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 adjacent tab. 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:

superkingdom
kingdom
phylum
class
order
family
genus
species

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".

Sub-species

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.

Loading sunburst data...

Tree controls

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The tree shows the occurrence of this domain across different species. More...

Species trees

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.

Interactive tree

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

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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.

Structures

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 Peptidase_S26 domain has been found. There are 25 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.

Loading structure mapping...

AlphaFold Structure Predictions

The list of proteins below match this family and have AlphaFold predicted structures. Click on the protein accession to view the predicted structure.

Protein	Predicted structure	External Information
A0A044VDS0	View 3D Structure	Click here
A0A077Z8U8	View 3D Structure	Click here
A0A077ZQ06	View 3D Structure	Click here
A0A0D2GXD0	View 3D Structure	Click here
A0A0D2H662	View 3D Structure	Click here
A0A0H3GTU0	View 3D Structure	Click here
A0A0J9XRL3	View 3D Structure	Click here
A0A0K0DT33	View 3D Structure	Click here
A0A0K0E2C5	View 3D Structure	Click here
A0A0K0JPX0	View 3D Structure	Click here
A0A0N4U1W8	View 3D Structure	Click here
A0A0P0VT29	View 3D Structure	Click here
A0A0R0GQS6	View 3D Structure	Click here
A0A158Q461	View 3D Structure	Click here
A0A175W963	View 3D Structure	Click here
A0A175WDL4	View 3D Structure	Click here
A0A1C1C9Q7	View 3D Structure	Click here
A0A1C1CCN0	View 3D Structure	Click here
A0A1D6EFB1	View 3D Structure	Click here
A0A1D6F845	View 3D Structure	Click here
A0A1D6GGF0	View 3D Structure	Click here
A0A1D6H558	View 3D Structure	Click here
A0A1D6I0D8	View 3D Structure	Click here
A0A1D6I5Q0	View 3D Structure	Click here
A0A1D6JNR1	View 3D Structure	Click here
A0A1D6L5X4	View 3D Structure	Click here
A0A1D6L610	View 3D Structure	Click here
A0A1D6NB37	View 3D Structure	Click here
A0A1D6PQA1	View 3D Structure	Click here
A0A1D8PN24	View 3D Structure	Click here
A0A2R8PY00	View 3D Structure	Click here
A0A368UMI2	View 3D Structure	Click here
A0A3P7E5Q0	View 3D Structure	Click here
A0A3Q0KCW1	View 3D Structure	Click here
A0A5K1K8B7	View 3D Structure	Click here
A0A5K4EAL6	View 3D Structure	Click here
A4ICW7	View 3D Structure	Click here
B4FU77	View 3D Structure	Click here
B6UIG2	View 3D Structure	Click here
C0NFE8	View 3D Structure	Click here

Showing 40 matches

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Family: Peptidase_S26 (PF10502)

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