Biochemical and structural characterization of the putative dihydropteroate synthase ortholog Rv1207 of Mycobacterium tuberculosis.

Dihydropteroate synthase (DHPS) is involved in de novo biosynthesis of the essential cofactor folate by catalyzing the condensation of para-aminobenzoic acid (pABA) and 6-hydroxymethyl-7,8-dihydropterin-pyrophosphate (H2PtPP). Mycobacterium tuberculosis possesses a functional DHPS (MtDHPS, Rv3608c, folP1) and, based on sequence similarities, a putative ortholog (Rv1207, folP2). Here, we demonstrate that Rv1207 shows a low H2PtPP substrate affinity and lacks enzymatic DHPS activity. However, we found dapsone, a structural analog of pABA and clinically used DHPS inhibitor, to weakly bind both proteins. To gain insights into the lack of DHPS activity of Rv1207, its three-dimensional structure was determined at 2.64 A. The overall fold of both, MtDHPS (1EYE) and Rv1207, is highly conserved and conforms to a classical triosephosphate isomerase barrel arrangement. The predicted H2PtPP-binding pocket of Rv1207 is occupied by a histidine side chain, relative to a leucine residue in MtDHPS, consistent with the low affinity for this substrate and the lack of DHPS activity. We conclude that folP2 does not encode a DHPS and therefore cannot act as bypass for folP1. The metabolic function of Rv1207 remains to be defined.