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J. Biol. Chem., Vol. 276, Issue 30, 28121-28125, July 27, 2001

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A Better Enzyme to Cope with Cold
COMPARATIVE FLEXIBILITY STUDIES ON PSYCHROTROPHIC, MESOPHILIC, AND THERMOPHILIC IPMDHS^*

Ádám Svingor, József Kardos^§, István Hajdú, Attila Németh, and Péter Závodszky^¶

From the  Institute of Enzymology, Biological Research Center, Hungarian Academy of Sciences, H-1113 Karolina út 29, Budapest, Hungary and the ^§ Department of Biochemistry, Eötvös University, H-1088 Puskin út 3, Budapest, Hungary

3-Isopropylmalate dehydrogenase (IPMDH) from the psychrotrophic bacterium Vibrio sp. I5 has been expressed in Escherichia coli and purified. This cold-adapted enzyme is highly homologous with IPMDHs from other organisms, including mesophilic E. coli and thermophilic Thermus thermophilus bacteria. Its molecular properties are similar to these counterparts. Whereas the E. coli and T. thermophilus enzymes are hardly active at room temperature, the Vibrio IPMDH has reasonable activity below room temperature. The thermal stabilities, conformational flexibilities (hydrogen-deuterium exchange), and kinetic parameters of these enzymes were compared. The temperature dependence of the catalytic parameters of the three enzymes show similar but shifted profiles. The Vibrio IPMDH is a much better enzyme at 25 °C than its counterparts. With decreasing temperature i.e. with decreasing conformational flexibility, the specific activity reduces, as well; however, in the case of the Vibrio enzyme, the residual activity is still high enough for normal physiological operation of the organism. The cold-adaptation strategy in this case is achieved by creation of an extremely efficient enzyme, which has reduced but still sufficient activity at low temperature.

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