Abstract
Background : Mycobacterium ulcerans, the causative agent of Buruli ulcer in humans, is unique among the members ofMycobacteriumgenus due to the presence of the virulence determinant megaplasmid pMUM001. This plasmid encodesmultiple virulence-associated genes, includingmup011, which is an uncharacterized Ser/Thr protein kinase (STPK) PknQ.Methodology/Principal Findings : In this study, we have characterized PknQ and explored its interaction with MupFHA(Mup018c), a FHA domain containing protein also encoded by pMUM001. MupFHA was found to interact with PknQ andsuppress its autophosphorylation. Subsequent protein-protein docking and molecular dynamic simulation analyses showedthat this interaction involves the FHA domain of MupFHA and PknQ activation loop residues Ser170and Thr174. FHA domainsare known to recognize phosphothreonine residues, and therefore, MupFHA may be acting as one of the few unusual FHA-domain having overlapping specificity. Additionally, we elucidated the PknQ-dependent regulation of MupDivIVA(Mup012c), which is a DivIVA domain containing protein encoded by pMUM001. MupDivIVA interacts with MupFHA and thisinteraction may also involve phospho-threonine/serine residues of MupDivIVA.Conclusions/Significance : Together, these results describe novel signaling mechanisms inM. ulceransand show a three-way regulation of PknQ, MupFHA, and MupDivIVA. FHA domains have been considered to be only pThr specific and ourresults indicate a novel mechanism of pSer as well as pThr interaction exhibited by MupFHA. These results signify the needof further re-evaluating the FHA domain –pThr/pSer interaction model. MupFHA may serve as the ideal candidate forstructural studies on this unique class of modular enzymes.