Increased thermal stability against irreversible inactivation of XXXX dehydrogenase induced by decreased van der Waals volume at the subunit interface.

@entity1522 @entity70605 @entity526 @entity70603 @entity535 @entity46829 @entity1853 @entity70604 @entity70607 @entity3881 @entity70606
We have investigated factors affecting stability at the subunit-subunit interface of the dimeric enzyme @entity46829 dehydrogenase (IPMDH) from @entity3881 . Site-directed mutagenesis was used to replace @entity1853 256, a key residue in the subunit interaction, with other @entity1522 . Thermal stability against irreversible inactivation of the mutated enzymes was examined by analyzing the residual activity after heat treatment. The mutations @entity70603 and @entity70604 increased thermostability by 2.0 and 6.0 degrees C, respectively, whereas the mutations @entity70605 and @entity70606 had no effect. Thermostability of the @entity70607 mutated enzyme was 4.0 degrees C lower than that of the wild-type enzyme. To our surprise, increasing the hydrophobicity of residue 256 within the hydrophobic core of the enzyme resulted in a lower thermal stability. The mutated enzymes showed an inverse correlation between thermostability and the volume of the side chain at position 256. Based on the X-ray crystallographic structure of @entity526 IPMDH, the environment around M256 in the @entity3881 homolog is predicted to be sterically crowded. These results suggest that Met256 prevents favorable packing. Introduction of a smaller @entity535 at position 256 improves the packing and stabilizes the dimeric structure of IPMDH. The van der Waals volume of the @entity535 residue at the hydrophobic subunit interface is an important factor for maintaining the stability of the subunit-subunit interface and is not always optimized in the mesophilic IPMDH enzyme.
