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48  structures 1779  species 0  interactions 2807  sequences 13  architectures

Family: T2SSG (PF08334)

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

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Type II secretion system (T2SS), protein G 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 [1,2]. The T2SG family includes proteins such as EpsG (P45773) in Vibrio cholera, XcpT also called PddA (Q00514) in Pseudomonas aeruginosa or PulG (P15746)in Klebsiella pneumoniae. The PulG is thought to be anchored in the inner membrane with its C-terminus directed towards the periplasme [3]. Together with other members of the Type II secretion machinery, it is thought to assemble into a pilus-like structure that may function as a dynamic mechanism to push secreted proteins out of the cell. The polypeptide is organized into a long N-terminal alpha-helix followed by a loop region that separates it from a C-terminal anti-parallel beta-sheet [1].

Literature references

  1. Kohler R, Schafer K, Muller S, Vignon G, Diederichs K, Philippsen A, Ringler P, Pugsley AP, Engel A, Welte W; , Mol Microbiol 2004;54:647-664.: Structure and assembly of the pseudopilin PulG. PUBMED:15491357 EPMC:15491357

  2. Bally M, Filloux A, Akrim M, Ball G, Lazdunski A, Tommassen J; , Mol Microbiol 1992;6:1121-1131.: Protein secretion in Pseudomonas aeruginosa: characterization of seven xcp genes and processing of secretory apparatus components by prepilin peptidase. PUBMED:1588814 EPMC:1588814

  3. Reyss I, Pugsley AP; , Mol Gen Genet 1990;222:176-184.: Five additional genes in the pulC-O operon of the gram-negative bacterium Klebsiella oxytoca UNF5023 which are required for pullulanase secretion. PUBMED:2129543 EPMC:2129543

  4. 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

  5. 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

  6. 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

This tab holds annotation information from the InterPro database.

InterPro entry IPR013545

This entry represents the C-terminal domain of GspG.

GspG is the major pseudopilin of the type 2 secretion systems (T2SSs). The N-terminal hydrophobic helices of the GspG subunits arrange within the core of the pseudopilus, with the C-terminal domains and the Ca2+-binding sites located at the surface. The structure of GspG (also known as PulG) has been revealed [ PUBMED:28993624 ].

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 ].

Domain organisation

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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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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_1144 (release 18.0)
Previous IDs: GSPII_G; T2SG;
Type: Family
Sequence Ontology: SO:0100021
Author: Fenech M , Desvaux M
Number in seed: 78
Number in full: 2807
Average length of the domain: 104.9 aa
Average identity of full alignment: 37 %
Average coverage of the sequence by the domain: 68.32 %

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 21.0 21.0
Trusted cut-off 21.0 21.0
Noise cut-off 20.9 20.9
Model length: 108
Family (HMM) version: 14
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 T2SSG domain has been found. There are 48 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