Exploring Mechanisms of Cell Shape Control in Helicobacter pylori

Abstract

Helicobacter pylori chronically infects over half of the global population and is associated with increased risk for gastric cancer, the third leading cause of cancer deaths worldwide. H. pylori resides in the gastric mucosa of the human stomach where it utilizes helical cell shape to efficiently colonize the epithelium. However, the underlying molecular mechanisms that H. pylori bacteria use to generate and control their helical cell shape are not known. In this dissertation, I took a multidisciplinary approach using genetic, biochemical, and proteomic approaches to discover and characterize protein interactions among known cell shape determining (Csd) proteins to gain mechanistic insight into helical cell shape determination. We discovered that the non-enzymatic protein Csd5 comprises a multi-protein “Shapeosome” complex that resides in the cytoplasmic membrane where it interacts with ATP synthase, a cytoplasmic peptidoglycan synthase (MurF), a bacterial cytoskeleton protein (CcmA), and the bacterial cell wall. We also performed structure-function studies of Csd5 and the peptidoglycan hydrolase Csd4 to identify functional domains required for protein function. Finally, we show that H. pylori isolates obtained from a chronically infected host exhibit significant heterogeneity in cell shape and find that mutations in cell shape determining genes contribute to this cell shape diversity.