Research Article

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

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Science  01 Nov 2019:
Vol. 366, Issue 6465, pp. 589-593
DOI: 10.1126/science.aay0934

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Itaconate brings metalloenzyme to a halt

Controlled radicals enable unusual enzymatic transformations, but radical generation and management require dedicated systems. Ruetz et al. investigated how the immunometabolite itaconate might undermine these intricate systems to inhibit propionate metabolism, a crucial metabolic pathway in pathogenic Mycobacterium tuberculosis (Mtb) (see the Perspective by Boal). They found that the coenzyme A (CoA) derivative of itaconate can irreversibly inhibit the enzyme methylmalonyl-CoA mutase (MCM), which uses the radical-generating cofactor adenosylcobalamin, or coenzyme B12. Itaconyl-CoA derails the normal radical reaction catalyzed by MCM, forming a long-lived, biradical species, which is incapable of completing the catalytic cycle and cannot be recycled by the endogenous coenzyme B12 regeneration machinery. Itaconate blocks Mtb growth on propionate, and this inhibition mechanism may be relevant to how macrophages resist Mtb infection.

Science, this issue p. 589; see also p. 574

Abstract

Itaconate is an immunometabolite with both anti-inflammatory and bactericidal effects. Its coenzyme A (CoA) derivative, itaconyl-CoA, inhibits B12-dependent methylmalonyl-CoA mutase (MCM) by an unknown mechanism. We demonstrate that itaconyl-CoA is a suicide inactivator of human and Mycobacterium tuberculosis MCM, which forms a markedly air-stable biradical adduct with the 5′-deoxyadenosyl moiety of the B12 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.

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