Separable Roles for ATPase Domains Involved in Virulence Factor Secretion

Abstract

Pathogenic bacteria utilize specialized protein secretion machinery in order to either affect their host cells or to alter the bacterial cell surface itself. One such emerging secretion system, originally described in Mycobacterium tuberculosis, has been termed the Type VII secretion system (T7S) in bacteria. This system is defined in part by the presence of membrane-associated FtsK/SpoIIIE-like AAA-ATPase domain containing proteins, each containing multiple active sites. While presumed to be involved in the secretion of the virulence proteins, the function of the ATPases has not been previously determined. Furthermore, the broader family of these secretion systems includes gene clusters where the FtsK/SpoIIIE-like protein is split and coded by two genes rather than one. Here we explore the role of these ATPases in protein secretion using two T7S systems, one with a single ATPase and the other with a naturally split ATPase. Using complementary biochemical and in vivo assays, we demonstrate that the ATPases are essential for protein secretion. Further, we find that the active sites contribute differentially to substrate interaction and export, thus suggesting a novel system in which a subset of the ATPase domains may function as their own adapter molecules.