NMR Structural Studies of Type III Secretion System Tip Proteins

Abstract

The type III secretion system (T3SS) is a complex set of regulatory and structural protein machinery common to many Gram-negative bacteria for virulence. Many of these bacterial species are human pathogens and cause a variety of infectious diseases. These resulting diseases can be fatal and range from chronic infections of the lungs in cystic fibrosis patients from Pseudomonas aeruginosa infection to gastroenteritis from Salmonella typhimurium. Each of these species uses the T3SS to deliver bacterial effector proteins into the host cell cytosol in order to manipulate normal host cell functions. The purpose of these host cell alterations varies widely between bacterial species, including prevention of phagocytosis, evasion of host immune response, or even bacterial intracellularization. This variation in consequences for the host can largely be attributed to the many unique effector proteins between species (more than 100 have been identified), however, the proteins components of the type III secretion apparatus (T3SA) used to transfer these effectors are both structurally and functionally conserved. As there are still gaps in the current knowledge of how some of these T3SS proteins interact to regulate T3SA assembly and effector secretion, both structural and functional studies of these proteins are essential. In the work presented in this thesis, NMR studies and biophysical methods were used to characterize the interactions of T3SS tip proteins of S. typhimurium and P. aeruginosa with previously identified binding partners implicated in secretion control.