Trimming Fat Upon Infection: Proteolytic Demyristoylation as a Novel Bacterial Pathogenic Strategy

Host-pathogen interaction is a complex process that involves an array of molecular tools on both sides of the conflict. In the light of growing antibiotics resistance, understanding of virulence factors utilized by pathogenic bacteria is crucial for developing better treatment for infectious diseases. Shigella spp are food-borne bacterial pathogens and are one of the leading causes of bacterial dysentery worldwide. Similarly to other gram-negative pathogens, Shigella injects effector proteins into an infected cell to control its responses. Dedicated type III secretion system delivers more than twenty effectors which highjack normal cell signaling by modulating activity of host proteins. By interfering with immune signaling, cytoskeleton, and other pathways, effector proteins promote survival of the bacterial pathogen. Inability to secrete effectors severely attenuates Shigella spp, pointing to the crucial role of these proteins in pathogenesis. Therefore, gaining an insight into the mechanism of action of secreted effectors may hold a key to better understanding and treatment of infectious diseases. Here I characterized the Shigella flexneri secreted virulence factor IpaJ. I found that IpaJ is a cysteine protease with novel specificity. IpaJ cleaves a myristoylated amino-terminal glycine of host proteins and therefore irreversibly delipidates them. Although IpaJ can target multiple host proteins, it strongly favors members of ADP-ribosylation factors family (ARF) and related ARF-like (ARL) proteins. By inactivating ARF and ARL proteins, IpaJ disrupts the Golgi structure and prevents secretion through general secretory pathway. I also found that by blocking protein export from the endoplasmic reticulum, IpaJ suppresses the activation of immune signaling pathways. In summary, I characterized a novel virulence factor of Shigella spp, IpaJ. I have shown that IpaJ promotes bacterial pathogenesis and therefore may be of potential interest for therapeutic interventions. The biochemical analysis of the enzyme provides the first look at the mechanism of substrate recognition and highlights the potential use of IpaJ as a research tool to study protein N-myristoylation and the mechanisms of membrane trafficking.