Investigating the roles of T224 and T232 in the oxidation of cinnamaldehyde catalyzed by myxobacterial CYP260B1

Solvent isotope effects in the catalytic cycle of P450 CYP17A1: Computational modeling of the hydroxylation and lyase reactions

The catalytic cycle of the cytochromes P450 (CYP) requires two electrons from a protein redox partner and two protons from water to generate the main catalytic intermediate, a ferryl-oxo complex with π-cation on the heme porphyrin ring, termed Compound 1. The protonation steps are at least partially rate-limiting, therefore the steady-state rates of P450 catalysis are usually slower in deuterated solvent (D2O) by a factor of 1.5-3. However, in several P450 systems a pronounced inverse kinetic solvent isotope effect (KSIE ∼0.4-0.7) is observed, where the reaction is faster in D2O. This raises an important mechanistic question: Is this inverse solvent isotope effect compatible with Compound 1 catalyzed reactions, or is it indicative of another catalytic intermediate being involved? In this communication we use exhaustive numerical modeling of the P450 steady-state kinetics to demonstrate that a significant inverse KSIE cannot be obtained for a pure Compound 1 driven catalytic cycle of P450. Rather, an alternative, protonation independent, catalytic intermediate needs to be introduced. This result is applicable to the broad spectrum of P450s in nature, but as an example we use the extensively documented inverse isotope effect in the human steroid biosynthetic P450 CYP17A1 where the involvement of a heme peroxo anion intermediate has been characterized. Based on this analysis, we show that the observation of an inverse KSIE can be used as a general mechanistic probe for reaction cycle intermediates in the cytochromes P450.

Importance of Asparagine 202 in Manipulating Active Site Structure and Substrate Preference for Human CYP17A1

The multifunctional cytochrome P450 17A1 (CYP17A1) plays a crucial role in human steroid hormone synthesis (UniProtKB─P05093). It first carries out standard monooxygenase chemistry, converting pregnenolone (PREG) and progesterone (PROG) into 17OH-PREG and 17OH-PROG, utilizing a "Compound I" to initiate hydrogen abstraction and radical recombination in the classic "oxygen rebound" mechanism. Additionally, these hydroxylated products also serve as substrates in a second oxidative cycle which cleaves the 17-20 carbon-carbon bond to form dehydroepiandrosterone and androstenedione, which are key precursors in the generation of powerful androgens and estrogens. Interestingly, in humans, with 17OH-PREG, this so-called lyase reaction is more efficient than with 17OH-PROG, based on Kcat/Km values. In the present work, the asparagine residue at 202 position was replaced by serine, an alteration which can affect substrate orientation and control substrate preference for the lyase reaction. First, we report studies of solvent isotope effects for the N202S CYP17A1 mutant in the presence of 17OH-PREG and 17OH-PROG, which suggest that the ferric peroxo species is the predominant catalytically active intermediate in the lyase step. This conclusion is further supported by employing a combination of cryoradiolysis and resonance Raman techniques to successfully trap and structurally characterize the key reaction intermediates, including the peroxo, the hydroperoxo, and the crucial peroxo-hemiketal intermediate. Collectively, these studies show that the mutation causes active site structural changes that alter the H-bonding interactions with the key Fe-O-O fragment and the degree of protonation of the reactive ferric peroxo intermediate, thereby impacting lyase efficiency.

Sesquiterpenoids Produced by Combining Two Sesquiterpene Cyclases with Promiscuous Myxobacterial CYP260B1

Sesquiterpenes represent a class of important terpenoids with high structural diversity and a wide range of applications. The cyclized core skeletons are generated by sesquiterpene cyclases, and the structural diversity is further increased by a series of modification steps. Cytochromes P450 (P450s) are a class of monooxygenases and one of the main contributors to the structural diversity of natural products. Some of these P450s show a broad substrate range and might be promising candidates for the implementation of cascade reactions. In this study, a combinatorial biosynthesis approach was utilized by the combination of a promiscuous myxobacterial P450 (CYP260B1) with two sesquiterpene cyclases (FgJ01056, FgJ09920) of filamentous fungi. Two oxygenated products, culmorin and culmorone, and a new compound, koraidiol, were successfully generated and characterized. This approach suggests the potential use of noncognate P450s to produce novel oxygenated terpenoids, or to generate a novel biosynthetic route for known terpenoids by a combinatorial biosynthesis strategy.

CYP260B1 acts as 9α-hydroxylase for 11-deoxycorticosterone

Steroids and their oxyfunctionalized counterparts are valuable compounds for the pharmaceutical industry; however, the regio- and stereoselective introduction of oxygen is a challenging task for the synthetic chemistry. Thus, cytochromes P450 play an important role for the functionalization of steroidal compounds. In this study, we elucidated the main product of 11-deoxycorticosterone conversion formed by CYP260B1 from Sorangium cellulosum So ce56 as 9α-OH 11-deoxycorticosterone by NMR spectroscopy. This is, to the best of our knowledge, the first identification of a 9α-hydroxylase for this substrate. In addition, the major side product was identified as 21-OH pregna-1,4-diene-3,20-dione. Studies using 1α-OH 11-deoxycorticosterone as substrate suggested that the major side product is formed via dehydrogenation reaction. This side reaction was considerably decreased by employing the CYP260B1-T224A mutant, which showed an increased selectivity of about 75% compared to the 60% of the wild type for the 9α-hydroxylation. To scale up the production, an E. coli based whole-cell system harboring the CYP260B1-T224A variant as well as two heterologous redox partners was used. Employing growing cells in minimal medium led to a productivity of about 0.25g/l/d at a 50ml scale showing the biotechnological potential of this system.