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Engineering of halophilic enzymes: two acidic amino acid residues at the carboxy-terminal region confer halophilic characteristics to Halomonas and Pseudomonas nucleoside diphosphate kinases

¹ Kagoshima University;
² Alliance Protein Laboratories

(RECEIVED April 8, 2008; ACCEPTED June 13, 2008)

Nucleoside diphosphate kinase from Halomonas sp. 593 (HaNDK) exhibits halophilic characteristics. Residues 134 and 135 in the carboxy-terminal region of HaNDK are Glu-Glu, while those of its homologous counterpart of non-halophilic Pseudomonas NDK (PaNDK) are Ala-Ala. The double mutation, E134A-E135A, in HaNDK results in the loss of the halophilic characteristics and, conversely, the double mutation of A134E-A135E in PaNDK confers halophilic characters to this enzyme, indicating that the charged state of these two residues that are located in the C-terminal region plays a critical role in determining halophilic characteristics. The importance of these two residues vs. the net negative charges will be discussed in relation to the halophilicity of NDK.

Keywords: Halomonas; halophilic; negative charge; nucleoside diphosphate kinase; reversibility; solubility

³ E-mail: tokunaga{at}chem.agri.kagoshima-u.ac.jp

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