Decarboxylation and Protonation Enigma in the H85Q Mutant of Cytochrome P450 OleT .

Cytochrome P450 OleT (CYP450 OleT ), a member of CYP450 peroxygenases, catalyzes unusual decarboxylation activity. Unlike other members of the peroxygenases family, CYP450 OleT possesses a histidine at the 85th position, which was supposed to be the root cause of the decarboxylation activity in CYP450 OleT . This work addresses the His85 → Gln mutant paradox, where mutation of His → Gln still shows efficient decarboxylation activity in CYP450 OleT . The MD simulation of the H85Q mutant of CYP450 OleT shows that in the absence of the histidine at the 85th position, an Asp239 plays a similar role via a well-organized water channel. Our simulation shows that such a water channel is vital for the optimal substrate positioning needed for the decarboxylation activity and is gated by the Q85-N242 residue pair. Interestingly, the MD simulation of the WT CYP450BSβ shows a closed channel that blocks access to the Glu236 (analogous residue to Asp239 in CYP450 OleT ), and therefore, CYP450BSβ shows low decarboxylation activity.