Itaconyl-CoA forms a stable biradical in methylmalonyl-CoA mutase and derails its activity and repair.

Itaconate is an immunometabolite with both anti-inflammatory and bactericidal effects. Its coenzyme A (CoA) derivative, itaconyl-CoA, inhibits B-dependent methylmalonyl-CoA mutase (MCM) by an unknown mechanism. We demonstrate that itaconyl-CoA is a suicide inactivator of human and MCM, which forms a markedly air-stable biradical adduct with the 5'-deoxyadenosyl moiety of the B coenzyme. Termination of the catalytic cycle in this way impairs communication between MCM and its auxiliary repair proteins. Crystallography and spectroscopy of the inhibited enzyme are consistent with a metal-centered cobalt radical ~6 angstroms away from the tertiary carbon-centered radical and suggest a means of controlling radical trajectories during MCM catalysis. Mycobacterial MCM thus joins enzymes in the glyoxylate shunt and the methylcitrate cycle as targets of itaconate in pathogen propionate metabolism.