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1  structure 473  species 0  interactions 563  sequences 6  architectures

Family: T2SSB (PF16537)

Summary: Type II secretion system protein B

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Type II secretion system protein B Provide feedback

This is the B protein from some operons of bacterial secretion systems of type II. The exact function of the B protein is not known, though in the case of Vibrio cholerae there is a fusion protein between proteins A and B that includes an AAA domain, a PG_binding domains well as this domain at the C-terminus [2]. Many of the other species have no A or B domain genes in this operon. The type II secretion pathway is conserved in Gram-negative bacteria that are prevalent in bacterial pathogens of plants (Pseudomonas fluorescens, Erwinia or Xanthomonas species), animals (Aeromonas hydrophila) and humans (Klebsiella oxytoca, Pseudomonas aeruginosa, Vibrio cholerae or Legionella pneumophila). Typical type II secretion systems (T2SSs) are encoded by a set of 12 to 16 gsp (general secretion pathway) genes organised into large operons including the conserved 'core' genes denoted C to O and in some bacterial species, as indicated above, extra gsp genes such as gspAB, gspN or gspS. A different nomenclature is used for Pseudomonas T2SSs, so the B gene is referred to as the P protein [1].

Literature references

  1. Korotkov KV, Sandkvist M, Hol WG;, Nat Rev Microbiol. 2012;10:336-351.: The type II secretion system: biogenesis, molecular architecture and mechanism. PUBMED:22466878 EPMC:22466878

  2. Martynowski D, Grochulski P, Howard PS;, Acta Crystallogr D Biol Crystallogr. 2013;69:142-149.: Structure of a periplasmic domain of the EpsAB fusion protein of the Vibrio vulnificus type II secretion system. PUBMED:23385451 EPMC:23385451

Internal database links

This tab holds annotation information from the InterPro database.

InterPro entry IPR032389

GspB is an accessory component of the type II secretion system (T2SS). Together with GspA, it contribute to GspD assembly and transport to the outer membrane possibly by increasing the pore size of the peptidoglycan or anchoring it to this structural meshwork [ PUBMED:30767847 ].

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 PilP (CL0655), which has the following description:

The clan contains the following 3 members:



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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...


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Curation and family details

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Seed source: Jackhmmer:P20725.2
Previous IDs: T2SB;
Type: Family
Sequence Ontology: SO:0100021
Author: Coggill P
Number in seed: 42
Number in full: 563
Average length of the domain: 59 aa
Average identity of full alignment: 29 %
Average coverage of the sequence by the domain: 21.9 %

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 28.4 28.4
Trusted cut-off 28.4 28.4
Noise cut-off 28.1 28.3
Model length: 60
Family (HMM) version: 8
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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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 T2SSB domain has been found. There are 1 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
A0A0H3GMT1 View 3D Structure Click here
Q01563 View 3D Structure Click here