ACTIN in ACTION · Actin-based motility of intracellular human pathogens

Actin and its associated regulatory proteins are fundamental components of the cytoskeleton, playing a central role in nearly every process in eukaryotes. Remarkably, the intracellular pathogens Shigella and Listeria have evolved specialized proteins, known as effectors, to hijack this crucial system of the host. These effectors induce actin polymerization on the bacterial surface, allowing the pathogens to propel themselves within and between host cells through a process called actin-based motility (ABM). Despite the critical role of ABM in bacterial infections, the mechanism by which ABM effectors interact with and activate host cell proteins is not understood at the atomic level. In addition, the regulation mechanisms of ABM and the host cell response to the cytoskeletal manipulation remain unclear.I therefore propose to elucidate the mechanisms of actin regulation during intoxication by ABM effectors. Using single-particle cryo-EM and cryo-electron tomography — techniques that have only become widely accessible in the past decade — I will determine the first high-resolution structures of ABM effectors and their complexes with actin-regulatory proteins. Building on my extensive expertise in studying actin and its associated proteins with these cutting-edge methods, I will develop a detailed mechanistic model of how ABM effectors orchestrate and regulate the host cytoskeleton, as well as how host cell proteins influence ABM within the cellular environment. Hypothesizing that cytoskeletal modulation by ABM effectors triggers cellular responses, I will employ a combination of proteomics and transcriptomics analyses to decipher how this manipulation of the actin cytoskeleton impacts host cell response pathways.This study will provide atomic-level insights into actin cytoskeleton regulation during bacterial infection, laying the groundwork for developing targeted therapies against diseases like shigellosis and listeriosis, which pose major medical challenges.