Crystal structures of mutants of Thermus thermophilus IPMDH adapted to lowtemperatures

Random mutagenesis on thermophilic 3-isopropylmalate dehydrogenases (IPMDH; EC 1.1.1.85) produced mutant enzymes which adapt to low temperatures. Thes e mutants had higher activity at lower temperatures than the wildtype enzym e without losing high thermostability. Here we report three structures of t he mutants of Thermus thermophilus IPMDH determined by X-ray diffraction wh ich was adapted to a low-temperature environment. Two of them have unstable coenzyme binding states and the other one probably has a stable substrate binding state. The present research suggests that the adaptation is correla ted with the binding of either coenzyme or the substrate.