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This review covers our current knowledge on catalytically self-sufficient cytochromes P450. These enzymes present all the advantages of the regio- and stereo-selectivity of typical P450s combined with the fact that, due to the natural fusion with their reductases, their application in biocatalysis does not need the addition of other proteins: only NAD(P)H and substrate are needed to trigger catalysis. To this date only few catalytically self-sufficient P450s have been isolated from bacteria, fungi and plants. Their low number does not detract from their importance, as the reactions they catalyse and the turnover numbers of which they are capable (in some cases higher than 15,000 s−1) makes them highly relevant to the chemical and pharmaceutical industry. These enzymes will be covered in this review, together with their specific reactions relevant to the field of biocatalysis.

ABSTRACTAntimicrobial resistance is a global issue currently resulting in the deaths of hundreds of thousands of people a year worldwide. Data present in the literature illustrate the emergence of many bacterial species that display resistance to known antibiotics; Acinetobacterspp. are a good example of this. We report here that Acinetobacter radioresistenshas a Baeyer-Villiger monooxygenase (Ar-BVMO) with 100% amino acid sequence identity to the ethionamide monooxygenase of multidrug-resistant (MDR) Acinetobacter baumannii. Both enzymes are only distantly phylogenetically related to other canonical bacterial BVMO proteins. Ar-BVMO not only is capable of oxidizing two anticancer drugs metabolized by human FMO3, danusertib and tozasertib, but also can oxidize other synthetic drugs, such as imipenem. The latter is a member of the carbapenems, a clinically important antibiotic family used in the treatment of MDR bacterial infections. Susceptibility tests performed by the Kirby-Bauer disk diffusion method demonstrate that imipenem-sensitive Escherichia coliBL21 cells overexpressing Ar-BVMO become resistant to this antibiotic. An agar disk diffusion assay proved that when imipenem reacts with Ar-BVMO, it loses its antibiotic property. Moreover, an NADPH consumption assay with the purified Ar-BVMO demonstrates that this antibiotic is indeed a substrate, and its product is identified by liquid chromatography-mass spectrometry to be a Baeyer-Villiger (BV) oxidation product of the carbonyl moiety of the β-lactam ring. This is the first report of an antibiotic-inactivating BVMO enzyme that, while mediating its usual BV oxidation, also operates by an unprecedented mechanism of carbapenem resistance.

Arbuscular (AM) mycorrhizal fungi form symbiotic associations with the roots of plants that lead to increased growth and health of many plants. The agricultural application of mycorrhizas has remained difficult since AM fungi are obligate biotrophs that show only very limited growth in the absence of a host. As a first step in the molecular and genetic characterization of these fungi we have constructed genomic libraries of Glomus versiforme and Gigaspora margarita. We demonstrated that in addition to fungal genes these libraries contain clones derived from the genome of endosymbiotic bacteria that are present in fungal spores. A genomic clone encoding elongation factor 1 alpha (EF-1) was isolated from G. versiforme and to our knowledge this is the first time a low copy number gene was cloned from an AM fungus. The EF-1 promoter is highly active in mycorrhizal roots and will be an important tool for the expression of foreign genes in the fungus.