Characterization of an acyl‐CoA: carboxylate CoA‐transferase from Aspergillus nidulans involved in propionyl‐CoA detoxification

Summary Filamentous fungi metabolize toxic propionyl‐CoA via the methylcitrate cycle. Disruption of the methylcitrate synthase gene leads to an accumulation of propionyl‐CoA and attenuates virulence of Aspergillus fumigatus . However, addition of acetate, but not ethanol, to propionate‐containing medium strongly reduces the accumulation of propionyl‐CoA and restores growth of the methylcitrate synthase mutant. Therefore, the existence of a CoA‐transferase was postulated, which transfers the CoASH moiety from propionyl‐CoA to acetate and, thereby, detoxifying the cell. In this study, we purified the responsible protein from Aspergillus nidulans and characterized its biochemical properties. The enzyme used succinyl‐, propionyl‐ and acetyl‐CoA as CoASH donors and the corresponding acids as acceptor molecules. Although the protein displayed high sequence similarity to acetyl‐CoA hydrolases this activity was hardly detectable. We additionally identified and deleted the coding DNA sequence of the CoA‐transferase. The mutant displayed weak phenotypes in the presence of propionate and behaved like the wild type when no propionate was present. However, when a double‐deletion mutant defective in both methylcitrate synthase and CoA‐transferase was constructed, the resulting strain was unable to grow on media containing acetate and propionate as sole carbon sources, which confirmed the in vivo activity of the CoA‐transferase.