Use of chemical auxiliaries to control p450 enzymes for predictable oxidations at unactivated C-h bonds of substrates

Selective biocatalytic hydroxylation of unactivated methylene C-H bonds in cyclic alkyl substrates

The cytochrome P450 monooxygenase CYP101B1 from Novosphingobium aromaticivorans selectively hydroxylated methylene C-H bonds in cycloalkyl rings. Cycloketones and cycloalkyl esters containing C6, C8, C10 and C12 rings were oxidised with high selectively on the opposite side of the ring to the carbonyl substituent. Cyclodecanone was oxidised to oxabicycloundecanol derivatives in equilibrium with the hydroxycyclodecanones.

Strategies for Substrate-Regulated P450 Catalysis: From Substrate Engineering to Co-catalysis

Cytochrome P450 enzymes (P450s) catalyze the monooxygenation of various organic substrates. These enzymes are fascinating and promising biocatalysts for synthetic applications. Despite the impressive abilities of P450s in the oxidation of C-H bonds, their practical applications are restricted by intrinsic drawbacks, such as poor stability, low turnover rates, the need for expensive cofactors (e.g., NAD(P)H), and the narrow scope of useful non-native substrates. These issues may be overcome through the general strategy of protein engineering, which focuses on the improvement of the catalysts themselves. Alternatively, several emerging strategies have been developed that regulate the P450 catalytic process from the viewpoint of the substrate. These strategies include substrate engineering, decoy molecule, and dual-functional small-molecule co-catalysis. Substrate engineering focuses on improving the substrate acceptance and reaction selectivity by means of an anchoring group. The latter two strategies utilize co-substrate-like small molecules that either are proposed to reform the active site, thereby switching the substrate specificity, or directly participate in the catalytic process, thereby creating new catalytic peroxygenation capabilities towards non-native substrates. For at least 10 years, these approaches have played unique roles in solving the problems highlighted above, either alone or in conjunction with protein engineering. Herein, we review three strategies for substrate regulation in the P450-catalyzed oxidation of non-native substrates. Furthermore, we address remaining challenges and potential solutions associated with these approaches.

The Oxidation of Hydrophobic Aromatic Substrates by Using a Variant of the P450 Monooxygenase CYP101B1

The cytochrome P450 monooxygenase CYP101B1, from a Novosphingobium bacterium is able to bind and oxidise aromatic substrates but at a lower activity and efficiency than norisoprenoids and monoterpenoid esters. Histidine 85 of CYP101B1 aligns with tyrosine 96 of CYP101A1, which, in the latter enzyme forms the only hydrophilic interaction with its substrate, camphor. The histidine residue of CYP101B1 was mutated to phenylalanine with the aim of improving the activity of the enzyme for hydrophobic substrates. The H85F mutant lowered the binding affinity and activity of the enzyme for β-ionone and altered the oxidation selectivity. This variant also showed enhanced affinity and activity towards alkylbenzenes, styrenes and methylnaphthalenes. For example the rate of product formation for acenaphthene oxidation was improved sixfold to 245 nmol per nmol CYP per min. Certain disubstituted naphthalenes and substrates, such as phenylcyclohexane and biphenyls, were oxidised with lower activity by the H85F variant. Variants at H85 (A and G) designed to introduce additional space into the active site so as to accommodate these larger substrates did not improve the oxidation activity. As the H85F mutant of CYP101B1 improved the oxidation of hydrophobic substrates, this residue is likely to be in the substrate binding pocket or the access channel of the enzyme. The side chain of the histidine might interact with the carbonyl groups of the favoured norisoprenoid substrates of CYP101B1.

Exploring substrate promiscuity of chlorophenol hydroxylase against biphenyl derivatives

The substrate promiscuity of 2,4-dichlorophenol hydroxylase against biphenyl derivatives was explored. This enzyme may be used as a potentially useful catalyst in the bioremediation of aromatic contaminants.