Substitution of lysine with glutamic acid at position 193 in bovine CYP11A1 significantly affects protein oligomerization and solubility but not enzymatic activity.

CYP11A1, a mitochondrial cytochrome P450, catalyzes the conversion from cholesterol to pregnenolone, the crucial step in the steroid hormone biosynthesis of mammals. It was shown in prior investigations, that the putative F-G loop of this enzyme is involved in membrane attachment. We produced different bovine CYP11A1 variants by rational protein design and could show that a deletion of 20 amino acids comprising parts of the F-G loop results in an enzyme with a three-fold increased solubility, the highest solubility of a CYP11A1 variant obtained so far. Furthermore, a single amino acid mutation, K193E, could be identified which leads not only to a higher solubility of CYP11A1 as well as a 4-fold improved expression rate, but also lowers the oligomerization of the protein while its activity is only slightly decreased. Therefore, this mutant has many advantages for the biotechnological application of CYP11A1 and is an important step towards crystallization of this mitochondrial P450.