Download MendeleyStructural insight into G-protein chaperone-mediated maturation of a bacterial adenosylcobalamin-dependent mutase.
Vaccaro, F.A., Faber, D.A., Andree, G.A., Born, D.A., Kang, G., Fonseca, D.R., Jost, M., Drennan, C.L.(2023) J Biol Chem 299: 105109-105109
- PubMed: 37517695
- DOI: https://doi.org/10.1016/j.jbc.2023.105109
- Primary Citation of Related Structures:
8SSL, 8STA - PubMed Abstract:
G-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° 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'-[(β,γ)-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.
Organizational Affiliation:
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.
