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Nucleoside diphosphate kinase Group I (NDPk_I)-like: NDP kinase domains are present in a large family of structurally and functionally conserved proteins from bacteria to humans that generally catalyze the transfer of gamma-phosphates of a nucleoside triphosphate (NTP) donor onto a nucleoside diphosphate (NDP) acceptor through a phosphohistidine intermediate. The mammalian nm23/NDP kinase gene family can be divided into two distinct groups. The group I genes encode proteins that generally have highly homologous counterparts in other organisms and possess the classic enzymatic activity of a kinase. This group includes vertebrate NDP kinases A-D (Nm23- H1 to -H4), and its counterparts in bacteria, archea and other eukaryotes. NDP kinases exist in two different quaternary structures; all known eukaryotic enzymes are hexamers, while some bacterial enzymes are tetramers, as in Myxococcus. They possess the NDP kinase active site motif (NXXH[G/A]SD) and the nine residues that are most essential for catalysis.
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