Acetaldehyde–alcohol dehydrogenase (AdhE) enzymes are a key metabolic enzyme in bacterial physiology and pathogenicity. They convert acetyl-CoA to ethanol via an acetaldehyde intermediate during ethanol fermentation in an anaerobic environment. This two-step reaction is associated to NAD + regeneration, essential for glycolysis. The bifunctional AdhE enzyme is conserved in all bacterial kingdoms but also in more phylogenetically distant microorganisms such as green microalgae. It is found as an oligomeric form called spirosomes, for which the function remains elusive. Here, we use cryo-electron microscopy to obtain structures of Escherichia coli spirosomes in different conformational states. We show that spirosomes contain active AdhE monomers, and that AdhE filamentation is essential for its activity in vitro and function in vivo. The detailed analysis of these structures provides insight showing that AdhE filamentation is essential for substrate channeling within the filament and for the regulation of enzyme activity.
Acetaldehyde–alcohol dehydrogenase (AdhE) converts acetyl-CoA to ethanol and is a key enzyme in bacterial alcoholic fermentation. AdhE forms spirosomes and, here, the authors present the cryoEM structures of compact and extended E.coli AdhE spirosomes and show that the extended conformation is the catalytically active form of the enzyme and discuss mechanistic implications.