The virB-D4 Operon

The VirB-D4 T4SS in Bartonella consists of an operon with 10 genes (virB2-10 and the downstream-located virD gene), and is most closely related to a conjugation system encoded by the A. tumefaciens plasmid AT [72]. The VirB-D4 T4SS has been shown to mediate most of the virulence attributes associated with the interaction of B. henselae and human endothelial cells [73]. These include rearrangement of the actin cytoskeleton, resulting in the formation of bacterial aggregates and their internalization by the invasome structure; proinflammatory activation, leading to cell adhesion molecule expression and chemokine secretion; and inhibition of apoptotic cell death, resulting in enhanced endothelial cell survival. The virB effector molecules are encoded by a set of duplicated genes located immediately downstream of the virB operon [74]. The C-terminal of these Bartonella-trans-located effector proteins (Beps) harbors an intracellular delivery domain and a short, positively charged tail sequence that together constitutes a transfer signal.

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