The Structure Basis for Burkholderia pseudomallei Hcp-induced Multinucleated Giant Cell Formation

Abstract

The Type VI Secretion System cluster 1 (T6SS1) is essential for the pathogenesis of Burkholderia pseudomallei, the causative agent of melioidosis. Inside host cells, B. pseudomallei escapes into the cytosol and induces multinucleated giant cell (MNGC) formation through T6SS1. The hemolysin-coregulated protein 1 (Hcp1) is critical for T6SS1 secretion and function. We show that Hcp1 is detectable on the surface of infected cells and surface-bound Hcp1 increases MNGC formation upon bacterial infection. Hcp1 also forms hexameric rings and has a unique extended loop (Asp40-Arg56) that acts as key contact points between adjacent hexameric rings. Mutation of these residues prevents the formation of Hcp1 dodecamers, suggesting defective tube assembly. The mutated surface-bound Hcp1s suppress bacterial-induced MNGC formation. Infection with bacterial mutants carrying the aforementioned mutations abolishes MNGC formation and Hcp1 secretion. Therefore, these data reveal the novel contribution of Hcp1 in B. pseudomallei pathogenesis apart from its role in supporting T6SS secretion.