The transition metals tungsten and molybdenum are the heaviest metals found in biological systems and are embedded in the cofactor of several metalloenzymes. As a result of their redox activity, they provide great catalytic power in these enzymes and facilitate chemical reactions that would not occur using only the functionalities of natural amino acids. For their functionality these enzymes depend on a metal cofactor, which consists of at least one metal binding pterin (MPT) and a tungsten or molybdenum ion, but the complete make-up of the cofactor differs per enzyme group. One of these enzyme groups comprises the AOR-family enzymes. These enzymes have the ability to oxidize a range of aldehyde substrates into their corresponding carboxylic acid products. Next to this, they are also the only known catalysts able to perform the thermodynamically challenging reduction reaction of carboxylic acids to aldehydes. These enzymes are currently obtained by purification from the hyperthermophilic archaeon Pyrococcus furiosus. This process, however, does not yield a large amount of enzyme, since it is naturally expressed at moderate levels. For that reason, other production methods need to be considered if the enzyme is to be used on a large scale. These alternatives include the use of a recombinant expression system. The recombinant expression of W-dependent enzymes in different host organisms, such as Escherichia coli, has already been attempted for different enzymes, but with varying success. This shows that more research on the production, and especially incorporation of the metal cofactor, is necessary to achieve a successful production and use of recombinant AOR-family enzymes.

Terrestrial and oceanic geothermal areas emit substantial amounts of hydrocarbons in the form of methane and the short-chain alkanes ethane and propane. Under hydrothermal conditions, these alkanes can also be oxidised to their respective alcohols and ketones, with a preference for the 2-position. The thermoacidophilic verrucomicrobial methanotroph Methylacidiphilum fumariolicum SolV, isolated from the Solfatara volcano, was previously shown to oxidise methane as well as the short-chain hydrocarbons propane and ethane. Here, we show the growth of strain SolV on the C3 compounds 2-propanol and acetone with growth rates of 0.054 h⁻¹ and 0.042 h⁻¹, respectively. In contrast to methanotrophic growth (rate 0.07 h⁻¹), growth was not dependent on CO₂ or lanthanides. Respiration experiments on steady-state continuous cultures showed an apparent affinity of 0.4 μM acetone and 5.4 μM 2-propanol. Transcriptomic analysis of these cultures showed that a gene cluster including a novel acetone monooxygenase (PMO3), previously identified in the closely related species Methylacidiphilum caldifontis, was highly upregulated under growth on C3 substrates. These results support the versatile metabolism of verrucomicrobial methanotrophs. The conversion of other compounds besides methane can be important in view of the ecological relevance of methanotrophs.

More than ten ergot alkaloids comprising both natural and semi-synthetic products are used to treat various diseases. The central C ring forms the core pharmacophore for ergot alkaloids, giving them structural similarity to neurotransmitters, thus enabling their modulation of neurotransmitter receptors. The haem catalase chanoclavine synthase (EasC) catalyses the construction of this ring through complex radical oxidative cyclization. Unlike canonical catalases, which catalyse H2O2 disproportionation, EasC and its homologues represent a broader class of catalases that catalyse O2-dependent radical reactions. We have elucidated the structure of EasC by cryo-electron microscopy, revealing a nicotinamide adenine dinucleotide phosphate (reduced) (NADPH)-binding pocket and a haem pocket common to all haem catalases, with a unique homodimeric architecture that is, to our knowledge, previously unobserved. The substrate prechanoclavine unprecedentedly binds in the NADPH-binding pocket, instead of the previously suspected haem-binding pocket, and two pockets were connected by a slender tunnel. Contrary to the established mechanisms, EasC uses superoxide rather than the more generally used transient haem iron–oxygen complexes (such as compounds I, II and III), to mediate substrate transformation through superoxide-mediated cooperative catalysis of the two distant pockets. We propose that this reactive oxygen species mechanism could be widespread in metalloenzyme-catalysed reactions.

Peat particulate organic matter (POM) in the anoxic subsurface of peatlands is increasingly recognized as an important terminal electron acceptor (TEA) in anaerobic respiration. While POM reduction has been demonstrated in laboratory peat-soil incubations and (electro-) chemical reduction assays, direct demonstration of POM reduction in peat soils under in situ, field conditions involving quantification of transferred electrons remain missing. Herein, we demonstrate that deployment of an oxidized reference POM in the anoxic, methanogenic subsurface of three ombrotrophic bogs, followed by one year incubation, resulted in the transfer of approximately 150–170 μmol of electrons per gram POM to the deployed reference POM. The capacity of this reduced POM to accept electrons was partially restored upon subsequent exposure to dissolved oxygen. These findings provide direct evidence for POM acting as regenerable and sustainable TEA for anaerobic respiration in temporarily anoxic parts of peat soils. Based on the number of electrons transferred to POM and thermodynamic considerations, we estimate that anaerobic respiration to POM may largely suppress methanogenesis in peat soils, particularly close to the oxic-anoxic interface across which POM is expected to undergo redox cycling.