Cloning and Characterization of MDH from the Psychrophilic Bacterium, Aquaspirillum arcticum; Molecular Basis for Cold Adaptation
Sun-Yong KIM*a,b, Jae-Hwan LIMa,b, Ha-Jin SUNGb, Ye-Sun HANa, and Yunje CHOa
a Structural Biology Center, Korea Institute of Science and Technology, Seoul, Korea
b The Graduate School of Biotechnology, Korea University, Seoul, Korea
Aquaspirillum arcticum is a psychrophilic bacterium whose optimum growth temperature is 4℃. To understand the mechanisms of cold adaptation, we have purified, characterized and cloned the enzyme malate dehydrogenase (Aa MDH)(EC 1.1.1.37) from Aquaspirillum arcticum. The enzyme is composed of 328 amino acids, and its molecular mass is 35,122Da. We compared catalytic properties of Aa MDH with those of mesophilic, Escherichia coli, MDH (Ec MDH) and themorphilic, Thermus aquaticus, MDH(Ta MDH); Aa MDH was more heat-labile than Ec MDH and Ta MDH (the Tm value about 50℃). However, the catalytic efficiency was higher than Ec MDH and Ta MDH at low temperature (the Kcat/Km values of Aa MDH were a few fold higher than those of Ec MDH below 20℃). Despite of its high functional efficiency at low temperature, the amino acids sequence of Aa MDH was remarkably similar to that of Ta MDH. We will discuss the details of catalytic properties of Aa MDH and propose a few specific amino acids of Aa MDH that might play important roles for cold adaptation.
