Abstract: A challenge for microbial pathogens is to assure that their translocated
effector proteins target only the correct host cell compartment
during infection. The Legionella pneumophila effector
vacuolar protein sorting inhibitor protein D (VipD) localizes to
early endosomal membranes and alters their lipid and protein
composition, thereby protecting the pathogen from endosomal
fusion. This process requires the phospholipase A1 (PLA1) activity
of VipD that is triggered specifically on VipD binding to the host
cell GTPase Rab5, a key regulator of endosomes. Here, we present
the crystal structure of VipD in complex with constitutively active
Rab5 and reveal the molecular mechanism underlying PLA1 activation.
An active site-obstructing loop that originates from the Cterminal
domain of VipD is repositioned on Rab5 binding, thereby
exposing the catalytic pocket within the N-terminal PLA1 domain.
Substitution of amino acid residues located within the VipD?Rab5
interface prevented Rab5 binding and PLA1 activation and caused
a failure of VipD mutant proteins to target to Rab5-enriched endosomal
structures within cells. Experimental and computational analyses
confirmed an extended VipD-binding interface on Rab5,
explaining why this L. pneumophila effector can compete with cellular
ligands for Rab5 binding. Together, our data explain how the
catalytic activity of a microbial effector can be precisely linked to its
subcellular localization.
