Kinase-independent synthesis of 3-phosphorylated phosphoinositides by a phosphotransferase

Abstract

Despite their low abundance, phosphoinositides play a central role in membrane traffic and signalling. PtdIns(3,4,5)P₃ and PtdIns(3,4)P₂ are uniquely important, as they promote cell growth, survival and migration. Pathogenic organisms have developed means to subvert phosphoinositide metabolism to promote successful infection and their survival in host organisms. We demonstrate that PtdIns(3,4)P₂ is a major product generated in host cells by the effectors of the enteropathogenic bacteria Salmonella and Shigella. Pharmacological, gene silencing and heterologous expression experiments revealed that, remarkably, the biosynthesis of PtdIns(3,4)P₂ occurs independently of phosphoinositide 3-kinases. Instead, we found that the Salmonella effector SopB, heretofore believed to be a phosphatase, generates PtdIns(3,4)P₂ de novo via a phosphotransferase/phosphoisomerase mechanism. Recombinant SopB is capable of generating PtdIns(3,4,5)P₃ and PtdIns(3,4)P₂ from PtdIns(4,5)P₂ in a cell-free system. Through a remarkable instance of convergent evolution, bacterial effectors acquired the ability to synthesize 3-phosphorylated phosphoinositides by an ATP- and kinase-independent mechanism, thereby subverting host signalling to gain entry and even provoke oncogenic transformation.