Histidine 117 in the His-Gly-Ser-Asp motif is Required for the Biochemical Activities of Nucleoside Diphosphate Kinase of Mycobacterium smegmatis

Nucleoside diphosphate kinase (NDK), which is widely conserved in both prokaryotes and eukaryotes, maintains a balanced pool of nucleotide triphosphates and their deoxy derivatives. NDKs from bacterial and other systems contain the conserved HGSD motif, where the His residue is required for the biochemical activities, namely the NTPase (AT-Pase and GTPase), NTP synthesising, and autophosphorylation activities of the enzyme. Amino acid sequence homology comparison of the NDK of Mycobacterium smegmatis (MsmNDK) with the NDKs of other bacterial genera showed the presence of H(117)GSD motif. While the recombinant wild type MsmNDK showed the NTPase, NTP synthesising, and autophosphorylation activities, the H117Q mutation abolished the biochemical activities of the recombinant MsmNDK-H117Q mutant protein in vitro. These observations demonstrate that the H117 residue in the HGSD motif is required for the biochemical activities of MsmNDK.