Biology subjects

Belhamri, M.

Publications and source records attributed to Belhamri, M..

2 recordsLinked to original sources

bioRxiv2024

Snapshots of acetyl-CoA synthesis, the final step of CO2 fixation in the Wood-Ljungdahl pathway

In the ancient microbial Wood-Ljungdahl pathway, CO2 is fixed in a multi-step process ending with acetyl-CoA synthesis at the bifunctional carbon monoxide dehydrogenase/acetyl-CoA synthase complex (CODH/ACS). Here, we present catalytic snapshots of the CODH/ACS from the gas-converting acetogen Clostridium autoethanogenum, characterizing the molecular choreography of the overall reaction including electron transfer to the CODH for CO2 reduction, methyl transfer from the corrinoid iron-sulfur protein (CoFeSP) partner to the ACS active site and acetyl-CoA production. Unlike CODH, the multidomain ACS undergoes large conformational changes to form an internal connection to the CODH active site, accommodate the CoFeSP for methyl transfer and protect the reaction intermediates. Altogether, the structures allow us to draw a detailed reaction mechanism of this enzyme crucial for CO2 fixation in anaerobic organisms. One-Sentence Summary: Structural description of key states of CO2 fixation by the carbon monoxide dehydrogenase/acetyl-CoA synthase complex.

biophysics↗

bioRxiv2024

Carbon monoxide-driven bioethanol production operates via a tungsten-dependent catalyst

Microbial alcohol production from waste gasses is a game changer for sustainable carbon cycling and remediation. While the biotechnological process employing Clostridium autoethanogenum to transform syngas (H2/CO2/CO) is blooming, the reactions involved in ethanol biosynthesis remain to be demonstrated. Here, we experimentally showed that ethanol production initiates via a tungsten-dependent aldehyde:ferredoxin oxidoreductase (AFOR), which reduces acetate to acetaldehyde. Such an unfavourable reaction has often been considered unsuitable for a biological process. To answer this riddle, we demonstrated that the thermodynamic pull of CO-oxidation and ethanol synthesis is crucial for triggering acetate reduction. The experimental setup performed with native CO-dehydrogenase and AFOR highlighted the key role of ferredoxin in stimulating the activity of both metalloenzymes and electron shuttling. The crystal structure of holo AFOR refined to 1.59-[A] resolution, together with its biochemical characterisation, provides new insights into the reaction mechanism and the specificities of this enzyme fundamental to sustainable biofuel production.

biochemistry↗