Serine/threonine/tyrosine phosphorylation in bacterial cell regulation

            Protein phosphorylation on serine, threonine, and tyrosine residues was believed for many years not to occur in bacteria. Now, however, it is emerging as an important regulatory mechanism, affecting the growth and virulence of several pathogenic species. My lab identified the first tyrosine phosphatase that is required for bacterial survival, and we are pursuing genetic and biochemical studies to understand the role of this protein in Caulobacter.

            When cells are depleted of the tyrosine phosphatase homolog CtpA, they fail to separate during cell division and grow in short chains with numerous outer membrane blebs, after which they lose viability. Peptidoglycan sacculi isolated from CtpA-depleted cells are also connected in chains, indicating that these cells are unable to cleave their septal peptidoglycan. These phenotypes suggest that CtpA is normally involved in the synthesis or remodeling of cell envelope components such as peptidoglycan or lipopolysaccharide. We are using genetic screens and biochemical isolations to identify CtpA’s functional partners and targets. We are also analyzing the roles of other S/T/Y kinases and phosphatases encoded in the Caulobacter genome.