The pathogenic bacterium Clostridium difficile thrives by fermentation of L-leucine to ammonia, CO2, isovalerate, and isocaproate under anaerobic conditions. Ketyl radicals have been proposed to mediate a key reaction catalysed by an iron–sulphur cluster-containing dehydratase, which requires activation by ATP-dependent electron transfer from a second iron–sulphur protein. A kinetically competent product-related allylic ketyl radical bound to the dehydratase using electron paramagnetic resonance spectroscopy is identified. These results suggest that other 2-hydroxyacyl-CoA dehydratases (and the related benzoyl-CoA reductases) may employ ketyl radical intermediates. The absence of radical generators makes these enzymes unprecedented in biochemistry.
- Jihoe Kim
- Daniel J. Darley
- Antonio J. Pierik
