Visualization of a radical B12 enzyme with its G-protein chaperone.

Publication Type:

Journal Article


Proc Natl Acad Sci U S A, Volume 112, Issue 8, p.2419-24 (2015)


Apoproteins, Catalytic Domain, Coenzymes, Conserved Sequence, Crystallography, X-Ray, Cupriavidus, GTP Phosphohydrolases, GTP-Binding Proteins, Guanosine Diphosphate, Methylmalonyl-CoA Mutase, Mitochondrial Membrane Transport Proteins, Models, Molecular, Molecular Chaperones, Protein Binding, Protein Structure, Tertiary, Protein Subunits


<p>G-protein metallochaperones ensure fidelity during cofactor assembly for a variety of metalloproteins, including adenosylcobalamin (AdoCbl)-dependent methylmalonyl-CoA mutase and hydrogenase, and thus have both medical and biofuel development applications. Here, we present crystal structures of IcmF, a natural fusion protein of AdoCbl-dependent isobutyryl-CoA mutase and its corresponding G-protein chaperone, which reveal the molecular architecture of a G-protein metallochaperone in complex with its target protein. These structures show that conserved G-protein elements become ordered upon target protein association, creating the molecular pathways that both sense and report on the cofactor loading state. Structures determined of both apo- and holo-forms of IcmF depict both open and closed enzyme states, in which the cofactor-binding domain is alternatively positioned for cofactor loading and for catalysis. Notably, the G protein moves as a unit with the cofactor-binding domain, providing a visualization of how a chaperone assists in the sequestering of a precious cofactor inside an enzyme active site. </p>

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