title: Visualization of a radical B12 enzyme with its G-protein chaperone.
abstract: 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.
authors: Department of Chemistry and.
authors: Marco
authors: M
authors: Jost
authors: Department of Biological Chemistry, University of Michigan, Ann Arbor, MI 48109-0600.
authors: Valentin
authors: V
authors: Cracan
authors: Department of Chemistry and.
authors: Paul A
authors: PA
authors: Hubbard
authors: Department of Biological Chemistry, University of Michigan, Ann Arbor, MI 48109-0600.
authors: Ruma
authors: R
authors: Banerjee
authors: Department of Chemistry and Department of Biology, Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, MA 02139; and cdrennan@mit.edu.
authors: Catherine L
authors: CL
authors: Drennan
mesh_terms: D001059:Apoproteins / Q000737:chemistry / Q000378:metabolism; D020134:Catalytic Domain; D003067:Coenzymes / Q000378:metabolism; D017124:Conserved Sequence; D018360:Crystallography, X-Ray; D049921:Cupriavidus / Q000201:enzymology*; D020558:GTP Phosphohydrolases / Q000737:chemistry; D019204:GTP-Binding Proteins / Q000737:chemistry* / Q000378:metabolism*; D006153:Guanosine Diphosphate / Q000737:chemistry / Q000378:metabolism; D008765:Methylmalonyl-CoA Mutase / Q000737:chemistry* / Q000378:metabolism*; D033681:Mitochondrial Membrane Transport Proteins / Q000737:chemistry; D008958:Models, Molecular; D018832:Molecular Chaperones / Q000737:chemistry* / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism
chemical_list: D001059:Apoproteins; D003067:Coenzymes; D033681:Mitochondrial Membrane Transport Proteins; D018832:Molecular Chaperones; D021122:Protein Subunits; D006153:Guanosine Diphosphate; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins; D008765:Methylmalonyl-CoA Mutase
keywords: G protein; crystallography; metallochaperone; metallocofactor delivery; vitamin B12