Structural insight into the Mycobacterium tuberculosis Rv0020c protein and its interaction with the PknB kinase

The protein Rv0020c from Mycobacterium tuberculosis, also called FhaA, is one of the major substrates of the essential Ser/Thr protein kinase (STPK) PknB. The protein is composed of three domains and is phosphorylated on a unique site in its N terminus. We solved the solution structure of both N- and C-terminal domains and demonstrated that the approximately 300 amino acids of the intermediate domain are not folded. We present evidence that the FHA, a phosphospecific binding domain, of Rv0020c does not interact with the phosphorylated catalytic domains of PknB, but with the phosphorylated juxtamembrane domain that links the catalytic domain to the mycobacterial membrane. We also demonstrated that the degree and the pattern of phosphorylation of this juxtamembrane domain modulates the affinity of the substrate (Rv0020c) toward its kinase (PknB).