Regulation of Peptidoglycan Synthesis and Hydrolysis in Streptococcus pneumoniae

• Main Author: Rued, Britta E
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2018
• Subjects: Biochemistry; Genetics; Microbiology; Pathology; Public health
• ISBN: 9780438755291; 0438755294

Streptococcus pneumoniae is a Gram-positive, opportunistic pathogen that represents a major threat to human health. The development of new therapeutics against this pathogen is vital and necessitates understanding of cell wall (peptidoglycan, PG) synthesis. PG gives rise to the distinct ovoid-shape of S. pneumoniae and is formed by simultaneous PG synthesis and hydrolytic remodeling. My thesis work focuses on three regulators of these processes in S. pneumoniae: GpsB, StkP, and FtsEX. In this thesis, I demonstrate that GpsB balances septal and peripheral (side-wall like) PG synthesis in S. pneumoniae and that protein Ser/Thr phosphorylation by the kinase StkP is modulated by GpsB. The presented results support a model in which GpsB negatively regulates peripheral PG synthesis and positively regulates septal ring closure via interactions with specific penicillin binding proteins. The second part of my thesis focuses on the protein complex FtsEX and its coordination of PG hydrolysis and divisome assembly in S. pneumoniae. In many bacteria, ABC-transporter-like FtsEX activates PG hydrolases. In S. pneumoniae, FtsEX activates the PG hydrolase PcsB. Using NMR, I determined that the helical lobe of the large extracellular loop of FtsX directly interacts with PcsB. This interaction interface is required in bacterial cells, as disruption of the interface causes cell defects. Additional experiments demonstrate that FtsEX is not just important for coordinating PcsB PG hydrolysis but also for divisome assembly. By examining the localization of fluorescently tagged division proteins during FtsX depletion, I discovered that FtsEX is required for proper divisome assembly and localization of specific proteins to the complex. FtsEX thus acts as a bridge between PG hydrolysis and divisome assembly in S. pneumoniae. The studies presented in this thesis provide further understanding of how these essential components of the S. pneumoniae divisome coordinate synthesis and hydrolysis of peptidoglycan.