Molecular modeling of the hamster adrenal P450C17.

The cytochrome P450C17 (C17) is the steroidogenic enzyme responsible for the conversion of pregnenolone and progesterone to dehydroepiandrosterone (DHEA) and Delta (4)-androstenedione (AD) respectively. This conversion is achieved by two enzymatic activities, 17 alpha -hydroxylase and 17,20-lyase, located at the same active site. In man, the adrenal C17 basically only produces DHEA. We have shown that the hamster adrenal C17 produces DHEA as well as AD. Moreover, the hamster like man produces cortisol as its major glucocorticoid. We can thus compare the hamster and human adrenal C17, and use their differences in order to elaborate a strategy for structure-function studies. We have thus engineered hamster adrenal C17 mutants which possess modified enzymatic activities. We also proceeded to elaborate a three-dimensional model of the hamster C17 to visualise the structural impact of these mutations. This model demonstrates that the mutations created are not localised at the active site, but rather in surrounding regions. These could affect the conformation of the active site, in turn, modulating the 17 alpha -hydroxylase and 17,20-lyase activities. For example, the mutation T202N is located next to Val 482 and Val 483 which compose the roof of the active site. This mutation decreased both 17 alpha -hydroxylase and 17,20-lyase activities, indicating the importance of the roof of the active site for general functionality of the C17.