title: Crystal structure of CobK reveals strand-swapping between Rossmann-fold domains and molecular basis of the reduced precorrin product trap.
abstract: CobK catalyzes the essential reduction of the precorrin ring in the cobalamin biosynthetic pathway. The crystal structure of CobK reveals that the enzyme, despite not having the signature sequence, comprises two Rossmann fold domains which bind coenzyme and substrate respectively. The two parallel β-sheets have swapped their last β-strands giving a novel sheet topology which is an interesting variation on the Rossmann-fold. The trapped ternary complex with coenzyme and product reveals five conserved basic residues that bind the carboxylates of the tetrapyrrole tightly anchoring the product. A loop, disordered in both the apoenzyme and holoenzyme structures, closes around the product further tightening binding. The structure is consistent with a mechanism involving protonation of C18 and pro-R hydride transfer from NADPH to C19 of precorrin-6A and reveals the interactions responsible for the specificity of CobK. The almost complete burial of the reduced precorrin product suggests a remarkable form of metabolite channeling where the next enzyme in the biosynthetic pathway triggers product release.
authors.affiliation: Chemistry &Biochemistry Department, School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London, E1 4NS, UK.
authors.forename: Shuang
authors.initials: S
authors.lastname: Gu
authors.affiliation: Chemistry &Biochemistry Department, School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London, E1 4NS, UK.
authors.forename: Oleksandr
authors.initials: O
authors.lastname: Sushko
authors.affiliation: School of Biosciences, University of Kent, Giles Lane, Canterbury, Kent CT2 7NJ, UK.
authors.forename: Evelyne
authors.initials: E
authors.lastname: Deery
authors.affiliation: School of Biosciences, University of Kent, Giles Lane, Canterbury, Kent CT2 7NJ, UK.
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Warren
authors.affiliation: Chemistry &Biochemistry Department, School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London, E1 4NS, UK.
authors.forename: Richard W
authors.initials: RW
authors.lastname: Pickersgill
mesh_terms: D001665:Binding Sites; D002384:Catalysis; D003067:Coenzymes / Q000737:chemistry / Q000378:metabolism; D018360:Crystallography, X-Ray; D020035:Holoenzymes / Q000737:chemistry / Q000378:metabolism; D006860:Hydrogen Bonding; D008958:Models, Molecular; D062105:Molecular Docking Simulation; D009249:NADP / Q000737:chemistry / Q000378:metabolism; D010088:Oxidoreductases / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D054730:Protein Interaction Domains and Motifs; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D013329:Structure-Activity Relationship; D013379:Substrate Specificity; D014578:Uroporphyrins / Q000737:chemistry* / Q000378:metabolism
chemical_list: D003067:Coenzymes; D020035:Holoenzymes; D014578:Uroporphyrins; D009249:NADP; D010088:Oxidoreductases