Type IV secretion system, VirB10 / TraB / TrbI (IPR005498)

Short name: T4SS_VirB10/TraB/TrbI

Overlapping homologous superfamilies


Family relationships



This entry represents type IV secretion system proteins VirB10, TraB and TrbI. Type IV secretion systems are found in plant and animal pathogens, as well as in symbiotic bacteria.

The tumour-inducing (Ti) plasmid of Rhizobium radiobacter (Agrobacterium tumefaciens) encodes various DNA transfer systems: VirB, Tra and Trb, where the virB operon is required for the transfer DNA to the plant host and the tra/trb systems are required for the conjugal transfer of the Ti plasmid between cells of Agrobacterium [PMID: 9679196, PMID: 12169609]. Of the two unlinked regions of octopine-type Ti plasmids that contain genes required for conjugal transfer, the tra gene cluster is probably required for conjugal DNA processing, whilst the other gene cluster, trb, probably directs the synthesis of a conjugal pilus and mating pore [PMID: 8763954]. It has been suggested that TraB extends into the periplasmic space and is anchored in the inner membrane via a single transmembrane segment near the N terminus. It is also thought that TraB may interact with TraP, in order to stabilise the proposed transmembrane complex formed by the tra operon products [PMID: 8655498].

The trbI gene encodes a 128-amino-acid polypeptide that is an intrinsic inner-membrane protein. TrbI may influence the kinetics of pilus outgrowth and/or retraction [PMID: 1355084]. Although not essential for conjugation, the TrbI protein greatly increases conjugational efficiency [PMID: 8763954]. In Plasmid pTiC58, all of the trb genes except trbI and trbK are essential for conjugal transfer [PMID: 10438776].

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.