Title: Threonine Phosphorylation Regulates Two-Component Systems Involved in Cell Wall Metabolism
Description: Bacteria must be able to respond and rapidly adapt to their environment. Historically, this has been studied in the context of two-component systems (TCS). TCS are composed of a sensor histidine kinase that upon activation autophosphorylates a conserved histidine residue and then transfers this phosphate to a response regulator at a conserved aspartate residue. This phosphorylation event leads to dimerization of the response regulator and its subsequent activation, which in many cases, is transcriptional activation. In addition to this classical signaling paradigm, bacteria also contain eukaryotic-like serine/threonine kinases (eSTK). In the past decade these kinases and their partner eukaryotic-like phosphatases have been characterized. However, their in vivo substrates still remain largely unknown. My thesis project describes how eukaryotic-like serine/threonine kinases regulate classical two-component systems involved in cell wall metabolism. In my first project, the Bacillus subtilis eSTK PrkC phosphorylates the essential response regulator WalR.

This modification enhances WalR activity and has pronounced transcriptional and physiological effects. I have also shown that this mechanism of regulation is conserved in the clinically relevant pathogen Staphylococcus aureus. My second project focuses on the role of Enterococcus faecalis eSTK IreK and its phosphorylation of the VanB-type vancomycin resistance histidine kinase VanS. My evidence suggests that threonine phosphorylation of IreK is required for full induction of the VanRS regulon genes and subsequently full vancomycin resistance. Together, these projects highlight how threonine phosphorylation of classical two-component systems is an important mechanism of regulation. Finally, I have done work with eSTKs from gram-negative bacteria and optimized conditions for their expression and activity in vitro.