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CYP63A2, a catalytically versatile fungal P450 monooxygenase capable of oxidizing higher-molecular-weight polycyclic aromatic hydrocarbons, alkylphenols, and alkanes
Khajamohiddin, S., A. Porollo, Y. Lam, P. Grimmett, AND J. Yadav. CYP63A2, a catalytically versatile fungal P450 monooxygenase capable of oxidizing higher-molecular-weight polycyclic aromatic hydrocarbons, alkylphenols, and alkanes. APPLIED AND ENVIRONMENTAL MICROBIOLOGY. American Society for Microbiology, Washington, DC, 79(8):2692-2702, (2013).
In this report we present a catalytically versatile P450 monooxygenase CYP63A2 from the model white-rot fungus Phanerochaete chrysosporium, which was found to catalyze the following unusual combination of oxidation reactions: a thermodynamically disfavored terminal carbon hydroxylation (ω-hydroxylation) in long-chain n-alkanes and alkylphenols and aromatic-ring hydroxylation in high-molecular weight polycyclic aromatic compounds.
Cytochrome P450 monooxygenases (P450s) are known to oxidize hydrocarbons albeit with limited substrate specificity across classes of these compounds. Here we report a P450 monooxygenase (CYP63A2) from the model ligninolytic white rot fungus Phanerochaete chrysosporium that was found to possess a broad oxidizing capability toward structurally diverse hydrocarbons belonging to mutagenic/carcinogenic fused-ring higher molecular weight polycyclic aromatic hydrocarbons (HMW-PAHs), endocrine-disrupting long-chain alkylphenols (APs), and crude oil aliphatic hydrocarbons n-alkanes. A homology-based 3D-model revealed presence of an extraordinarily large active site cavity in CYP63A2 compared to the mammalian PAH-oxidizing (CYP3A4, CYP1A2 and CYP1B1) and bacterial aliphatic hydrocarbon-oxidizing (CYP101D and CYP102A1) P450s. This structural feature in conjunction with ligand docking simulations suggested potential versatility of the enzyme. Experimental characterization using recombinantly expressed CYP63A2 revealed its ability to oxidize HMW-PAHs of varying ring size, including 4 rings (pyrene and fluoranthene), 5 rings [benzo(a)pyrene], and 6 rings [benzo(ghi)perylene]; the highest enzymatic activity being toward the 5-ring PAH followed by the 4-ring and 6-ring PAHs, in that order. CYP63A2 activity yielded monohydroxylated PAH metabolites. The enzyme was found to also act as an alkane ω hydroxylase that oxidized varying chain-length n-alkanes (C9-C12 and C15-C19) as well as alkyl side-chains (C3-C9) in alkylphenols (APs). CYP63A2 showed preferential oxidation of long chain-length APs and alkanes. To our knowledge, this is the first of its kind P450 across biological kingdoms that possesses such broad substrate specificity toward structurally diverse xenobiotics (PAHs, APs, and alkanes), making it a potent enzyme biocatalyst candidate to handle mixed pollution.