M.
tuberculosis GmhA
enzyme catalyzes the isomerization of D-
sedoheptulose 7-phosphate into D-glycero-D-α-manno-heptose-7-phosphate in
GDP-D-glycero-α-D-manno-heptose biosynthetic pathway. The D-glycero-α-D-manno-heptose is a major constituent of
lipopolysaccharide and contributes to virulence and antibiotic resistance to mycobacteria. In current study, we have performed the structural and biochemical analysis of M.
tuberculosis GmhA, the first
enzyme involved in D-
sedoheptulose 7-phosphate isomerization in
GDP-D-α-D-heptose biosynthetic pathway. The MtbGmhA
enzyme exits as tetramer and small angle X-ray scattering analysis also yielded tetrameric envelope in
solution. The MtbGmhA
enzyme binds to D-
sedoheptulose 7-phosphate with Km ~ 0.31 ± 0.06 mM-1 and coverts it to D-glycero-D-α-manno-heptose-7-phosphate with catalytic efficiency (kcat/Km) ~ 1.45 mM-1 s-1. The residues involved in D-
sedoheptulose 7-phosphate and Zn2+ binding were identified using modeled MtbGmhA + D-
sedoheptulose 7-phosphate + Zn2+ structure. To understand the role in catalysis, six site directed mutants of MtbGmhA were generated, which showed significant decrease in catalytic activity. The circular dichroism analysis showed ~ 46% α-helix, ~ 19% β-sheet and ~ 35% random coil structures of MtbGmhA
enzyme and melting temperature ~ 53.5 °C. Small angle X-ray scattering analysis showed the tetrameric envelope, which fitted well with modeled MtbGmhA tetramer in closed conformation. The MtbGmhA dynamics involved in D-
sedoheptulose 7-phosphate and Zn2+ binding was identified using dynamics simulation and showed enhanced stability in presence of these
ligands. Our biochemical data and structural knowledge have provided insight into mechanism of action of MtbGmhA
enzyme, which can be targeted for novel
antibiotics development against M.
tuberculosis.