Molecular mechanism of distinct salt-dependent enzyme activity of two halophilic nucleoside diphosphate kinasesYamamura, A., Ichimura, T., Kamekura, M., Mizuki, T., Usami, R., Makino, T., Ohtsuka, J., Miyazono, K., Okai, M., Nagata, K., Tanokura, M.
(2009) Biophys.J. 96: 4692-4700
- PubMed: 19486691
- DOI: 10.1016/j.bpj.2009.03.012
- PubMed Abstract:
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 ...
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.
Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan.