title: Structure of choline oxidase in complex with the reaction product glycine betaine.
abstract: Choline oxidase from Arthrobacter globiformis, which is involved in the biosynthesis of glycine betaine from choline, has been extensively characterized in its mechanistic and structural properties. Despite the knowledge gained on the enzyme, the details of substrate access to the active site are not fully understood. The `loop-and-lid' mechanism described for the glucose-methanol-choline enzyme superfamily has not been confirmed for choline oxidase. Instead, a hydrophobic cluster on the solvent-accessible surface of the enzyme has been proposed by molecular dynamics to control substrate access to the active site. Here, the crystal structure of the enzyme was solved in complex with glycine betaine at pH 6.0 at 1.95 Å resolution, allowing a structural description of the ligand-enzyme interactions in the active site. This structure is the first of choline oxidase in complex with a physiologically relevant ligand. The protein structures with and without ligand are virtually identical, with the exception of a loop at the dimer interface, which assumes two distinct conformations. The different conformations of loop 250-255 define different accessibilities of the proposed active-site entrance delimited by the hydrophobic cluster on the other subunit of the dimer, suggesting a role in regulating substrate access to the active site.
authors: Department of Chemistry, Georgia State University, PO Box 3965, Atlanta, GA 30302-3965, USA.
authors: Francesca
authors: F
authors: Salvi
authors: Department of Biology, Georgia State University, PO Box 4010, Atlanta, GA 30302-4010, USA.
authors: Yuan-Fang
authors: YF
authors: Wang
authors: Department of Chemistry, Georgia State University, PO Box 3965, Atlanta, GA 30302-3965, USA.
authors: Irene T
authors: IT
authors: Weber
authors: Department of Chemistry, Georgia State University, PO Box 3965, Atlanta, GA 30302-3965, USA.
authors: Giovanni
authors: G
authors: Gadda
mesh_terms: D000429:Alcohol Oxidoreductases / Q000737:chemistry* / Q000235:genetics; D001173:Arthrobacter / Q000737:chemistry* / Q000201:enzymology; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics; D001622:Betaine / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D057927:Hydrophobic and Hydrophilic Interactions; D008024:Ligands; D008958:Models, Molecular; D055503:Protein Multimerization; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry* / Q000235:genetics; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D008024:Ligands; D021122:Protein Subunits; D011994:Recombinant Proteins; D001622:Betaine; D000429:Alcohol Oxidoreductases; C019888:choline oxidase
keywords: choline oxidase; glucose–methanol–choline enzyme family; glycine betaine