The enzymes of β-lactam biosynthesis

Abstract

The β-lactam antibiotics and related β-lactamase inhibitors are amongst the most important small molecules in clinical use. Most, but not all, β-lactams including penicillins, cephalosporins, and clavulanic acid are produced via fermentation or via modification of fermented intermediates, with important exceptions being the carbapenems and aztreonam. The desire for more efficient routes to existing antibiotics and for access to new and synthetically challenging ones stimulates continued interest in β-lactam biosynthesis. We review knowledge of the pathways leading to β-lactam antibiotics focusing on the mechanisms, structures and biocatalytic applications of the enzymes involved.

Catalytic Mechanisms of Fe(II)- and 2-Oxoglutarate-dependent Oxygenases

“…1D, left) in addition to the desaturation reaction discussed above (20). Epimerization, unusual among the Fe(II)/2OG oxygenases, is redox-neutral (75), and this unprecedented reactivity has led to intensive studies to investigate the mechanism.…”

“…Of interest, substrates undergoing 1,2-dehydrogenation by Fe(II)/2OG-dependent oxygenases (including CAS, Fig. 1C) (20) all possess a heteroatom adjacent to the aliphatic C-C bond of interest. Additional experimental efforts are needed to further dissect these mechanisms.…”

“…A DAOCS⅐2OG⅐substrate ternary complex is proposed to react with O 2 to form a ferryl intermediate that initiates the reaction (32). One hydrogen atom is abstracted from the C2 ␤-methyl group of the substrate to produce a methylene radical, which undergoes rearrangement leading to ring expansion with the radical repositioned to the ternary carbon (C3), and then desaturation completes the reaction, perhaps by hydrogen atom transfer to the Fe(III)-OH (20,78). H6H is an enzyme isolated from Hyoscyamus niger (henbane) where it participates in the synthesis of scopolamine, a hallucinogenic tropane alkaloid.…”

“…The Fe(II)/2OG-dependent oxygenases catalyze a variety of oxidative transformations including hydroxylation, halogenation, ring closure, desaturation, epimerization, ring expansion, and epoxidation reactions. Because of their rich oxidative transformation capabilities, these enzymes play important roles in many biological processes (9) including the post-translational modification of collagen (11), fatty acid metabolism (12,13), oxygen sensing (14,15), DNA and RNA repair (16,17), demethylations related to epigenetic regulation (18,19), and the biosynthesis of many antibiotics and other secondary metabolites (20,21).…”

“…Chlorination is illustrated by SyrB2, acting on L-Thr that is covalently tethered via thioester linkage to a phosphopantetheine group on SyrB1 (28). Clavaminate synthase (CAS) is the paradigm for cyclization chemistry, transforming proclavaminate to dihydroclavaminic acid, but this trifunctional enzyme also catalyzes the hydroxylation of deoxyguanidinoproclavaminic acid and desaturation of dihydroclavaminic acid (20). Carbapenem synthase (CarC) is used to describe both desaturation and epimerization reactions (29,30).…”