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FIC-Mediated Post-Translational Modifications at the
Pathogen-Host Interface: Elucidating Structure, Function and Role in Infection

Final Report Summary - FICMODFUN (FIC-Mediated Post-Translational Modifications at thePathogen-Host Interface: Elucidating Structure, Function and Role in Infection)

The ubiquitous FIC domain catalyzes post-translational modifications (PTMs) of target proteins; i.e. AMPylation (=adenylylation) and, more rarely, uridylylation and phosphocholination. Fic proteins are thought to play critical roles in intrinsic signaling processes of prokaryotes and eukaryotes; however, a subset encoded by bacterial pathogens is translocated via dedicated secretion systems into the cytoplasm of mammalian host cells. Some of these host-targeted Fic proteins modify small GTPases leading to collapse of the actin cytoskeleton and other drastic cellular changes. Recently, we described a large set of functionally diverse homologues in pathogens of the genus Bartonella that are required for their “stealth attack” strategy and persistent course of infection. Only a few Fic proteins have been functionally characterized to date; our understanding of the functional plasticity of the FIC domain in mediating diverse target PTMs and their specific roles in infection thus remains limited. In this project, we have been studying the vast repertoire of host-targeted Fic proteins of Bartonella to: (i) identify novel target proteins and types of PTMs; (ii) study their physiological consequences and molecular mechanisms of action; and (iii) analyze structure-function relationships critical for FIC-mediated PTMs and infer from these data determinants of target specificity, type of PTM and mode of regulation. We have identified Rac-subfamily GTPases (Rac1/2/3 and RhoG) as AMPylation targets for the effector homologues Bep1, Bep197 and BepA of three different Bartonella lineages and deciphered for Bep1 the underlying molecular determinants of target selectivity amongst the highly conserved Rho-family GTPases. We further identified vimentin as AMPylation targets for Bep2 and GEF-H1 as target for BepC. Animal infection experiments have provided first indications to the individual contributions of FIC domain-containing effectors such as BepA, BepC and BepI to the establishment and course of intraerythrocytic bacteremia, which is corroborated with findings from cell culture infection experiments. Comparative genome analysis allowed us to identify a novel and independently evolved set of Beps in the recently described human pathogen Bartonella ancashensis which provided an additional resource for the identification of novel FIC domain-mediated effector functions in host cells to be explored in the course of this project.