Enzymatic versatility of the salmonella effector SopB enables manipulation of host phosphoinositide signalling.

Salmonella enterica relies on type III secreted effector proteins to invade host cells and establish an intracellular replicative niche, the Salmonella-containing vacuole (SCV). Among these effectors, SopB (also known as SigD) is notable for its functional versatility, contributing to virtually every stage of infection. Long characterized as a phosphoinositide phosphatase and inositol polyphosphate phosphatase, SopB was recently shown to also possess phosphotransferase activity, generating PtdIns(3,4)P2 (and, transiently, PtdIns(3,4,5)P3) de novo from PtdIns(4,5)P2 independently of PI 3-kinases and ATP. This discovery reframes how SopB activates the pro-survival kinase Akt and manipulates host signalling during invasion. Beyond its enzymatic activities, SopB engages the host Rho GTPases Cdc42 through a structurally distinct N-terminal domain and reorganizes the vimentin intermediate filament network to stabilize the SCV. In this review, we consider SopB as a paradigm for multifunctional effector biology, integrating its dual enzymatic activities, vimentin manipulation, anti-apoptotic signalling, and post-translational regulation into a unified model of how a single bacterial protein rewires host phosphoinositide metabolism across space and time.