VirB2

VirB2 is a small pilin protein that is a component of the type IV secretion system (T4SS) in Gram-negative bacteria, most notably the plant pathogen Agrobacterium tumefaciens. It forms the major structural subunits of the T-pilus, a filamentous appendage that mediates contact with plant cells and is involved in the transfer of DNA and proteins during conjugation and virulence.

VirB2 is encoded by the virB2 gene within the virB operon on the Ti plasmid. It is synthesized as a prepilin with an N-terminal leader sequence and is processed by a prepilin peptidase (PilD) to generate the mature pilin. The maturation typically involves removal of the leader peptide and often N-terminal modifications such as methylation, enabling polymerization into the pilus.

Mature VirB2 is a hydrophobic protein that polymerizes to form the extracellular T-pilus. Assembly occurs with the help of other virB gene products (VirB1, VirB4–VirB11), which constitute the secretion channel and pilus assembly machinery, guiding the incorporation of virB2 subunits into the growing pilus.

Functionally, the T-pilus assembled from VirB2 facilitates initial contact with plant cells and is required for efficient transfer of T-DNA and effector proteins. Consequently, VirB2 is essential for virulence in A. tumefaciens and related bacteria, contributing to the success of horizontal gene transfer and pathogenic interactions.

See also: Type IV secretion system, pilin, pilus, virulence.