OBJECTIVETo clone the gene encoding adenylate kinase of Thermus thermophilus HB27, an extremely thermophilic bacterium, express the protein in Escherichia coil and study the enzymatic characterization.

METHODSThe DNA fragment encoding adenylate kinase was obtained by PCR from the total DNA of Thermus thermophilus HB27 and cloned into the vector pET-28a. The recombinant plasmid was identified by PCR, restriction endonuclease digestion and sequence analysis. Enzymatic characterization of the expressed protein was carried out using spectrophotometric assays.

RESULTSThe gene coding for adenylate kinase from Thermus thermophilus HB27 was cloned and the protein was overexpressed in Escherichia coli BL21(DE3). The optimum reactive pH and temperature for the enzyme were 8.5 and 90 degrees celsius;, respectively. The Km of the recombinant adenylate kinase for ADP was 68.6 micromol/L, with an V(max)ADP of 0.294 mmol/(L.min). Under the condition of environmental temperature at 70, 80, 90, or 100 degrees celsius; for 7 h, the recombinant adenylate kinase still retained the enzymatic activity with high thermostability. AP5A, a specific adenylate kinase inhibitor, inhibited the enzymatic activity of the protein by 70% at the concentration of 2.0 mmol/L, with a Ki value of 46.39 micromol/L for ADP.

CONCLUSIONThe gene coding for adenylate kinase of Thermus thermophilus HB27 has been successfully cloned and expressed in Escherichia coil, which provides the basis for potential use of the highly thermostable recombinant HB27 adenylate kinase.