Understanding the structural basis of the selectivity of steroid hydroxylation
requires detailed structural and functional investigations on various steroid
hydroxylases with different selectivities, such as the bacterial cytochrome
P450 enzymes. Here, the crystal structure of the cytochrome P450
CYP106A1 from Priestia megaterium was solved. CYP106A1 exhibits a rare
additional structural motif of a cytochrome P450, a sixth β-sheet. The protein was found in different unusual conformations corresponding to both open
and closed forms even when crystallized without any known substrate. The
structural comparison of CYP106A1 with the previously investigated
CYP106A2, including docking studies for both isoforms with the substrate
cortisol, reveals a completely different orientation of the steroid molecule in
the active sites. This distinction convincingly explains the experimentally
observed differences in substrate conversion and product formation by the two
enzymes
