title: Axial Ligation and Redox Changes at the Cobalt Ion in Cobalamin Bound to Corrinoid Iron-Sulfur Protein (CoFeSP) or in Solution Characterized by XAS and DFT.
abstract: A cobalamin (Cbl) cofactor in corrinoid iron-sulfur protein (CoFeSP) is the primary methyl group donor and acceptor in biological carbon oxide conversion along the reductive acetyl-CoA pathway. Changes of the axial coordination of the cobalt ion within the corrin macrocycle upon redox transitions in aqua-, methyl-, and cyano-Cbl bound to CoFeSP or in solution were studied using X-ray absorption spectroscopy (XAS) at the Co K-edge in combination with density functional theory (DFT) calculations, supported by metal content and cobalt redox level quantification with further spectroscopic methods. Calculation of the highly variable pre-edge X-ray absorption features due to core-to-valence (ctv) electronic transitions, XANES shape analysis, and cobalt-ligand bond lengths determination from EXAFS has yielded models for the molecular and electronic structures of the cobalt sites. This suggested the absence of a ligand at cobalt in CoFeSP in α-position where the dimethylbenzimidazole (dmb) base of the cofactor is bound in Cbl in solution. As main species, (dmb)CoIII(OH2), (dmb)CoII(OH2), and (dmb)CoIII(CH3) sites for solution Cbl and CoIII(OH2), CoII(OH2), and CoIII(CH3) sites in CoFeSP-Cbl were identified. Our data support binding of a serine residue from the reductive-activator protein (RACo) of CoFeSP to the cobalt ion in the CoFeSP-RACo protein complex that stabilizes Co(II). The absence of an α-ligand at cobalt not only tunes the redox potential of the cobalamin cofactor into the physiological range, but is also important for CoFeSP reactivation.
authors.affiliation: Freie Universität Berlin, Department of Physics, 14195, Berlin, Germany.
authors.forename: Peer
authors.initials: P
authors.lastname: Schrapers
authors.affiliation: Freie Universität Berlin, Department of Physics, 14195, Berlin, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Mebs
authors.affiliation: Humboldt-Universität zu Berlin, Department of Biology, 10115, Berlin, Germany.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Goetzl
authors.affiliation: Humboldt-Universität zu Berlin, Department of Biology, 10115, Berlin, Germany.
authors.forename: Sandra E
authors.initials: SE
authors.lastname: Hennig
authors.affiliation: Freie Universität Berlin, Department of Physics, 14195, Berlin, Germany.
authors.forename: Holger
authors.initials: H
authors.lastname: Dau
authors.affiliation: Humboldt-Universität zu Berlin, Department of Biology, 10115, Berlin, Germany.
authors.forename: Holger
authors.initials: H
authors.lastname: Dobbek
authors.affiliation: Freie Universität Berlin, Department of Physics, 14195, Berlin, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Haumann
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D055598:Chemical Phenomena; D003035:Cobalt / Q000737:chemistry* / Q000378:metabolism; D045728:Corrinoids / Q000737:chemistry* / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D000068536:Bacillota / Q000378:metabolism; D007477:Ions / Q000737:chemistry / Q000378:metabolism; D007506:Iron-Sulfur Proteins / Q000737:chemistry* / Q000378:metabolism; D008024:Ligands; D008958:Models, Molecular; D010084:Oxidation-Reduction; D011485:Protein Binding; D011487:Protein Conformation; D012996:Solutions; D014805:Vitamin B 12 / Q000737:chemistry* / Q000378:metabolism; D056928:X-Ray Absorption Spectroscopy / Q000379:methods*
chemical_list: D001426:Bacterial Proteins; D045728:Corrinoids; D007477:Ions; D007506:Iron-Sulfur Proteins; D008024:Ligands; D012996:Solutions; C473700:corrin; D003035:Cobalt; D014805:Vitamin B 12