Heteroexpression and biochemical characterization of thermostable citrate synthase from the cyanobacteria Anabaena sp. PCC7120

The present study recombinantly expressed a citrate synthase from cyanobacteria Anabaena sp. PCC7120 (AnCS) in Escherichia coli and characterized its enzymatic activity. The molecular mass of native AnCS was 88,533.1 Da containing two 44,162.7 Da subunits. Recombinant AnCS revealed the highest activity at pH 9.0 and 25 degrees C. AnCS displayed high thermal stability with a half-life time (t(1/2)) of approximately 6.5 h at 60 degrees C, which was more thermostable than most CS from general organisms, but less than those from hyperthermophilic bacteria. The K-m values of oxaloacetate and acetyl-CoA were 138.50 and 18.15 mu M respectively, suggesting a higher affinity to acetyl-CoA than oxaloacetate. Our inhibition assays showed that AnCS activity was not severely affected by most metal ions, but was strongly inhibited by Cu2+ and Zn2+. Treatments with ATP, ADP, AMP, NADH, and DTT depressed the AnCS activity. Overall, our results provide information on the enzymatic properties of AnCS, which contributes to the basic knowledge on CS selection for industrial utilizations.