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25  structures 8561  species 0  interactions 23661  sequences 138  architectures

Family: Peptidase_S26 (PF10502)

Summary: Signal peptidase, peptidase S26

Pfam includes annotations and additional family information from a range of different sources. These sources can be accessed via the tabs below.

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

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.

  1. ^ 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
  2. ^ 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
  3. ^ Paetzel, M., Karla, A., Strynadka, N. C., and Dalbey, R. E. (2002b). Signal peptidases. Chem Rev 102, PP. 4549-4580
  4. ^ 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
  5. ^ 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

This page is based on a Wikipedia article. The text is available under the Creative Commons Attribution/Share-Alike License.

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

External database links

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.

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


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...

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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.

Representative proteomes UniProt
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Representative proteomes UniProt

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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.

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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...


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 View help on the curation process

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 View help on HMM parameters

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 Archea Eukaryota Eukaryota
Bacteria Bacteria Other sequences Other sequences
Viruses Viruses Unclassified Unclassified
Viroids Viroids Unclassified sequence Unclassified sequence


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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...

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


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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.

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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