The T6SS-5 VgrG spike protein mediates membrane fusion during intercellular spread by pseudomallei-group Burkholderia species.

Toesca IJ, French CT, Miller JF.

Citation

Toesca IJ, French CT, Miller JF. (2014) The T6SS-5 VgrG spike protein mediates membrane fusion during intercellular spread by pseudomallei-group Burkholderia species. Infection and Immunity

Abstract

Pseudomallei-group Burkholderia species are facultative intracellular parasites that efficiently spread from cell to cell by a mechanism involving fusion of adjacent cell membranes. Intercellular fusion requires the function of a type VI secretion system, T6SS-5, and its associated valine-glycine repeat protein, VgrG5. Here we show that VgrG5 alleles are conserved and functionally interchangeable between B. pseudomallei and its relatives B. mallei, B. oklahomensis, and B. thailandensis. We also demonstrate that the integrity of the VgrG5 C-terminal domain is required for fusogenic activity and identify sequence motifs, including two hydrophobic segments, that are important for fusion. Mutagenesis and secretion experiments using B. pseudomallei strains engineered to express T6SS-5 in vitro show that the VgrG5 C-terminal domain is dispensable for T6SS-mediated secretion of Hcp5, demonstrating that the ability of VgrG5 to mediate membrane fusion can be uncoupled from it’s essential role in type VI secretion. We propose a model that invokes a unique fusogenic activity at the C-terminus of VgrG5 that facilitates intercellular spread by B. pseudomallei and related species following injection across the plasma membranes of infected cells.