VirB7

VirB7 is a small lipoprotein component of certain Gram-negative bacterial type IV secretion systems (T4SS), most notably those encoded by the virB operon in Agrobacterium tumefaciens and related species. It is essential for the proper assembly and function of the T4SS, which mediates the transfer of DNA and protein substrates and the assembly of the T4SS pilus.

Locally, VirB7 is synthesized with an N-terminal signal peptide that directs lipid modification and insertion into the outer membrane. After processing by signal peptidase II, the N-terminal cysteine is lipidated, anchoring VirB7 to the periplasmic face of the outer membrane. In the mature complex, VirB7 forms a small subcomplex with VirB9 and VirB10, contributing to the core structure that spans both the inner and outer membranes.

Functionally, the VirB7–VirB9–VirB10 core complex stabilizes the secretion channel and participates in pilus assembly, facilitating the transfer of DNA and other substrates. Disruption of virB7 typically leads to reduced or abolished secretion and pilus formation, reflecting its structural role within the T4SS rather than a catalytic function.

Research highlights indicate that VirB7 interacts with VirB9 and VirB10 to form a conserved core component of the T4SS. Its small size and conserved presence across diverse T4SS-bearing bacteria underscore its fundamental role in the assembly and operation of these secretion systems.