Salmonella type III secretion: substrate targeting and injectisome assembly

The University of Utah was awarded a $728,244 Project Grant from the National Institute of Allergy and Infectious Diseases (NIAID) under the Allergy and Infectious Diseases Research program (CFDA 93.855) to conduct research on the molecular mechanisms of Salmonella's type III secretion system. The goal is to develop a better understanding of how this critical virulence mechanism in Gram-negative pathogens, including Salmonella, Shigella, Vibrio, Pseudomonas, Yersinia, and Chlamydia, selects and translocates effector proteins into host cells. By elucidating the core assembly and regulatory processes of these injectisome structures, the research aims to provide crucial knowledge to combat significant public health threats posed by these infectious bacteria.

Abstract

In the face of increasing antimicrobial resistance, understanding the mechanism of virulence factor(s) characteristics in bacteria is critical for developing new therapeutics. For many pathogens, large multi-protein molecular machines called injectisomes (also known as type III secretion systems) are central to pathogenesis. Injectisomes are central to virulence by many human pathogens including salmonella (gastroenteritis and typhoid fever), shigella (dysentery), vibrio (gastroenteritis) pseudomonas (diverse systemic infections), yersinia (plague), and chlamydia (sexually transmitted diseases), presenting significant health burdens. By understanding the mechanisms of injectisome biogenesis, function and coupled gene regulatory mechanisms, we poise ourselves to develop novel antimicrobial therapeutics. Although these pathogens are common, a barrier to fighting infections by injectisome-utilizing organisms has been incomplete structural insights into core mechanisms of secretion. Understanding these core mechanisms is crucial to developing novel anti-pathogen strategies. We propose experiments that provide fundamental knowledge about injectisome mechanisms for use in combating these significant pathogens. Understanding the molecular mechanisms controlling effector secretion will provide crucial knowledge toward combating injectisome-deploying pathogens. Type III secretion (T3S) is arguably the most important route through which gram-negative plant and animal pathogens translocate effector proteins into host cells and is a key component in bacterial symbiosis with eukaryotic organisms. There are beautiful structures lacking mechanisms of assembly with superficial knowledge of coupled gene regulatory systems that we will uncover. Our track-record on the related flagellar systems leaves no doubt that we are most qualified to do this. For more than twenty years, the selectivity of substrates for specific secretion by the injectisome-associated T3S systems from thousands of proteins produced in the cell has been an unsolvable mystery until now. T3S is the only secretion system in biology that undergoes a secretion- specificity switch from one class of secretion-substrates to a completely different class. Using newly devised genetic selections and screens we will determine how specific substrates are recognized and targeted for secretion by the salmonella pathogenicity island 1 (SPI1) T3S systems in coordination with SPI1 injectisome assembly and the secretion-specificity switch.