8ssl
From Proteopedia
Isobutyryl-CoA mutase fused Q341A in the presence of GTP
Structural highlights
FunctionICMF_CUPMC Catalyzes the reversible interconversion of isobutyryl-CoA and n-butyryl-CoA, and to a much lesser extent, of pivalyl-CoA and isovaleryl-CoA, using radical chemistry (PubMed:22167181). Also exhibits GTPase activity, associated with its G-protein domain (MeaI) that functions as a chaperone that assists cofactor delivery and proper holo-enzyme assembly (PubMed:22167181, PubMed:25675500). The G-domain of IcmF has also a role in its cofactor repair (PubMed:28130442). Does not display ATPase activity.[1] [2] [3] Publication Abstract from PubMedG-protein metallochaperones are essential for the proper maturation of numerous metalloenzymes. The G-protein chaperone MMAA in humans (MeaB in bacteria) uses GTP hydrolysis to facilitate the delivery of adenosylcobalamin (AdoCbl) to AdoCbl-dependent methylmalonyl-CoA mutase, an essential metabolic enzyme. This G-protein chaperone also facilitates the removal of damaged cobalamin (Cbl) for repair. Although most chaperones are standalone proteins, isobutyryl-CoA mutase fused (IcmF) has a G-protein domain covalently attached to its target mutase. We previously showed that dimeric MeaB undergoes a 180 degrees rotation to reach a state capable of GTP hydrolysis (an active G-protein state), in which so-called switch III residues of one protomer contact the G-nucleotide of the other protomer. However, it was unclear whether other G-protein chaperones also adopted this conformation. Here, we show that the G-protein domain in a fused system forms a similar active conformation, requiring IcmF oligomerization. IcmF oligomerizes both upon Cbl damage and in the presence of the nonhydrolyzable GTP analog, guanosine-5'-[(beta,gamma)-methyleno]triphosphate, forming supramolecular complexes observable by mass photometry and EM. Cryo-EM structural analysis reveals that the second protomer of the G-protein intermolecular dimer props open the mutase active site using residues of switch III as a wedge, allowing for AdoCbl insertion or damaged Cbl removal. With the series of structural snapshots now available, we now describe here the molecular basis of G-protein-assisted AdoCbl-dependent mutase maturation, explaining how GTP binding prepares a mutase for cofactor delivery and how GTP hydrolysis allows the mutase to capture the cofactor. Structural insight into G-protein chaperone-mediated maturation of a bacterial adenosylcobalamin-dependent mutase.,Vaccaro FA, Faber DA, Andree GA, Born DA, Kang G, Fonseca DR, Jost M, Drennan CL J Biol Chem. 2023 Sep;299(9):105109. doi: 10.1016/j.jbc.2023.105109. Epub 2023 , Jul 28. PMID:37517695[4] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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