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Publication Abstract from PubMed

Nucleoside diphosphate kinases from haloarchaea Haloarcula quadrata (NDK-q) and H. sinaiiensis (NDK-s) are identical except for one out of 154 residues, i.e., Arg(31) in NDK-q and Cys(31) in NDK-s. However, the salt-dependent activity profiles of NDK-q and NDK-s are quite different: the optimal NaCl concentrations of NDK-q and NDK-s are 1 M and 2 M, respectively. We analyzed the relationships of the secondary, tertiary, and quaternary structures and NDK activity of these NDKs at various salt concentrations, and revealed that 1), NDK-q is present as a hexamer under a wide range of salt concentrations (0.2-4 M NaCl), whereas NDK-s is present as a hexamer at an NaCl concentration above 2 M and as a dimer at NaCl concentrations below 1 M; 2), dimeric NDK-s has lower activity than hexameric NDK-s; and 3), dimeric NDK-s has higher helicity than hexameric NDK-s. We also determined the crystal structure of hexameric NDK-q, and revealed that Arg(31) plays an important role in stabilizing the hexamer. Thus the substitution of Arg (as in NDK-q) to Cys (as in NDK-s) at position 31 destabilizes the hexameric assembly, and causes dissociation to less active dimers at low salt concentrations.

Molecular mechanism of distinct salt-dependent enzyme activity of two halophilic nucleoside diphosphate kinases.,Yamamura A, Ichimura T, Kamekura M, Mizuki T, Usami R, Makino T, Ohtsuka J, Miyazono K, Okai M, Nagata K, Tanokura M Biophys J. 2009 Jun 3;96(11):4692-700. PMID:19486691^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.