Adjustment of conformational flexibility is a key event in the thermal adaptation of proteins.
3-Isopropylmalate dehydrogenase (IPMDH, E.C. 1.1.1.85) from the thermophilic bacterium Thermus thermophilus HB8 is homologous to IPMDH from the mesophilic Escherichia coli, but has an approximately 17 degreesC higher melting temperature. Its temperature optimum is 22-25 degreesC higher than that of the E. coli enzyme; however, it is hardly active at room temperature. The increased conformational rigidity required to stabilize the thermophilic enzyme against heat denaturation might explain its different temperature-activity profile. Hydrogen/deuterium exchange studies were performed on this thermophilic-mesophilic enzyme pair to compare their conformational flexibilities. It was found that Th. thermophilus IPMDH is significantly more rigid at room temperature than E. coli IPMDH, whereas the enzymes have nearly identical flexibilities under their respective optimal working conditions, suggesting that evolutionary adaptation tends to maintain a "corresponding state" regarding conformational flexibility. These observations confirm that conformational fluctuations necessary for catalytic function are restricted at room temperature in the thermophilic enzyme, suggesting a close relationship between conformational flexibility and enzyme function.
Závodszky
P
P
Institute of Enzymology, Biological Research Center, Hungarian Academy of Sciences, Pf. 7, H-1518 Budapest, Hungary.
Kardos
J
J
Svingor
Petsko
G A
GA
D050539:3-Isopropylmalate Dehydrogenase; D000429:Alcohol Oxidoreductases / Q000737:chemistry*; D002152:Calorimetry, Differential Scanning; D002384:Catalysis; D002942:Circular Dichroism; D017666:Deuterium Oxide; D004926:Escherichia coli; D006358:Hot Temperature; D011487:Protein Conformation; D017510:Protein Folding; D017550:Spectroscopy, Fourier Transform Infrared; D016963:Thermus thermophilus
D000429:Alcohol Oxidoreductases; D050539:3-Isopropylmalate Dehydrogenase; D017666:Deuterium Oxide