Phosphorylation of Mycobacterium tuberculosis Ser/Thr phosphatase by PknA and PknB

The integrated functions of 11 Ser/Thr protein kinases (STPKs) and one phosphatase manipulate the phosphorylation levels of critical proteins in Mycobacterium tuberculosis. In this study, we show that the lone Ser/Thr phosphatase (PstP) is regulated through phosphorylation by STPKs.

PstP is phosphorylated by PknA and PknB and phosphorylation is influenced by the presence of Zn(2+)-ions and inorganic phosphate (Pi). PstP is differentially phosphorylated on the cytosolic domain with Thr(137), Thr(141), Thr(174) and Thr(290) being the target residues of PknB while Thr(137) and Thr(174) are phosphorylated by PknA. The Mn(2+)-ion binding residues Asp(38) and Asp(229) are critical for the optimal activity of PstP and substitution of these residues affects its phosphorylation status. Native PstP and its phosphatase deficient mutant PstP(c) (D38G) are phosphorylated by PknA and PknB in E. coli and addition of Zn(2+)/Pi in the culture conditions affect the phosphorylation level of PstP. Interestingly, the phosphorylated phosphatase is more active than its unphosphorylated equivalent.

This study establishes the novel mechanisms for regulation of mycobacterial Ser/Thr phosphatase. The results indicate that STPKs and PstP may regulate the signaling through mutually dependent mechanisms. Consequently, PstP phosphorylation may play a critical role in regulating its own activity. Since, the equilibrium between phosphorylated and non-phosphorylated states of mycobacterial proteins is still unexplained, understanding the regulation of PstP may help in deciphering the signal transduction pathways mediated by STPKs and the reversibility of the phenomena.