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17  structures 1023  species 0  interactions 1194  sequences 3  architectures

Family: T2SSI (PF02501)

Summary: Type II secretion system (T2SS), protein I

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Type II secretion system (T2SS), protein I Provide feedback

The Type II secretion system, also called Secretion-dependent pathway (SDP), is responsible for the transport of proteins across the outer membrane first exported to the periplasm by the Sec or Tat translocon in Gram-negative (diderm) bacteria. As members of the T2SJ family, members of the T2SI family are pseudopilins containing prepilin signal sequences [1].

Literature references

  1. Howard SP, Critch J, Bedi A; , J Bacteriol 1993;175:6695-6703.: Isolation and analysis of eight exe genes and their involvement in extracellular protein secretion and outer membrane assembly in Aeromonas hydrophila. PUBMED:8407845 EPMC:8407845

  2. Desvaux M, Parham NJ, Scott-Tucker A, Henderson IR;, Trends Microbiol. 2004;12:306-309.: The general secretory pathway: a general misnomer?. PUBMED:15223057 EPMC:15223057

  3. Peabody CR, Chung YJ, Yen MR, Vidal-Ingigliardi D, Pugsley AP, Saier MH Jr;, Microbiology. 2003;149:3051-3072.: Type II protein secretion and its relationship to bacterial type IV pili and archaeal flagella. PUBMED:14600218 EPMC:14600218

  4. Desvaux M, Hebraud M, Talon R, Henderson IR;, Trends Microbiol. 2009;17:139-145.: Secretion and subcellular localizations of bacterial proteins: a semantic awareness issue. PUBMED:19299134 EPMC:19299134

External database links

This tab holds annotation information from the InterPro database.

InterPro entry IPR003413

This entry represent the C-terminal domain of GspI, which is a pseudopilin component of the type II secretion system (T2SS). It contains the prepilin signal sequences [ PUBMED:8407845 ]. In Pseudomonas aeruginosa GspI homologue, known as XcpV, has been suggested to be the central component and initiator of pseudopilus formation [ PUBMED:19828448 ].

The type II secretion system (T2SS) is one of several extracellular secretion systems in gram-negative bacteria. It delivers toxins and a range of hydrolytic enzymes including proteases, lipases and carbohydrate-active enzymes to the cell surface or extracellular space [ PUBMED:30767847 ]. T2SS systems are composed of 11 to 15 different proteins, which are generally called GspA to GspO and GspS. The T2SS spans the two bacterial membranes and ensures secretion of folded proteins across the outer membrane pore formed by GspD. The inner membrane complex contains GspC, GspL, GspM, and GspF. The cytoplasmic domains of GspL and GspF interact with an ATPase, GspE. GspE is thought to energize the formation of a short pseudopilus by several pilin-like proteins, GspG to GspK [ PUBMED:22523076 ]. GspD has been shown to interact with the inner membrane component GspC [ PUBMED:19217396 ].

The T2SS pseudopilus is a periplasmic filament composed of the major pseudopilin, EpsG, and four minor pseudopilins, EpsH, EpsI, EpsJ and EpsK. Pseudopilus is assembled by the polymerization of GspG (also known as PulG) subunits. Pseudopilin proteins have a conserved N-terminal hydrophobic segment followed by a more variable C-terminal periplasmic and globular domain [ PUBMED:28258547 ].

Gene Ontology

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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 Pilus (CL0327), which has the following description:

This clan contains bacterial and archaeal systems involved in flagellar or twitching motility, adhesion, protein secretion, and DNA uptake, such as type II secretion system (T2SS), the type IV pilus or the competence pilus (Com) [4]. Pili proteins enable the transfer of plasmid between bacteria. The families in this clan adopt an alpha helical structure which is packed against a beta sheet [2-3].

The clan contains the following 15 members:

Arch_flagellin Bundlin ComP_DUS GspH PilA4 Pilin Pilin_GH Pilin_PilX PilJ_C PilM PilS T2SSG T2SSI T2SSJ TcpA


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Representative proteomes UniProt

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

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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.

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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.

Curation View help on the curation process

Seed source: Pfam-B_2607 (release 5.4)
Previous IDs: GSPII_IJ; T2SI;
Type: Domain
Sequence Ontology: SO:0000417
Author: Mian N , Bateman A , Desvaux M
Number in seed: 97
Number in full: 1194
Average length of the domain: 79.4 aa
Average identity of full alignment: 24 %
Average coverage of the sequence by the domain: 61.15 %

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 25.0 25.0
Trusted cut-off 25.3 25.4
Noise cut-off 24.9 24.8
Model length: 80
Family (HMM) version: 20
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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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 T2SSI domain has been found. There are 17 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
A0A0H3GIF6 View 3D Structure Click here
P45760 View 3D Structure Click here
P45775 View 3D Structure Click here
Q00516 View 3D Structure Click here
Q32C41 View 3D Structure Click here
Q9I5P5 View 3D Structure Click here