title: Structural snapshots of MTA/AdoHcy nucleosidase along the reaction coordinate provide insights into enzyme and nucleoside flexibility during catalysis.
abstract: MTA/AdoHcy nucleosidase (MTAN) irreversibly hydrolyzes the N9-C1' bond in the nucleosides, 5'-methylthioadenosine (MTA) and S-adenosylhomocysteine (AdoHcy) to form adenine and the corresponding thioribose. MTAN plays a vital role in metabolic pathways involving methionine recycling, biological methylation, polyamine biosynthesis, and quorum sensing. Crystal structures of a wild-type (WT) MTAN complexed with glycerol, and mutant-enzyme and mutant-product complexes have been determined at 2.0A, 2.0A, and 2.1A resolution, respectively. The WT MTAN-glycerol structure provides a purine-free model and in combination with the previously solved thioribose-free MTAN-ADE structure, we now have separate apo structures for both MTAN binding subsites. The purine and thioribose-free states reveal an extensive enzyme-immobilized water network in their respective binding subsites. The Asp197Asn MTAN-MTA and Glu12Gln MTAN-MTR.ADE structures are the first enzyme-substrate and enzyme-product complexes reported for MTAN, respectively. These structures provide representative snapshots along the reaction coordinate and allow insight into the conformational changes of the enzyme and the nucleoside substrate. A "catalytic movie" detailing substrate binding, catalysis, and product release is presented.
authors.affiliation: Structural Biology and Biochemistry, Research Institute, Hospital for Sick Children, 555 University Avenue, Toronto, Ont., Canada.
authors.forename: Jeffrey E
authors.initials: JE
authors.lastname: Lee
authors.forename: G David
authors.initials: GD
authors.lastname: Smith
authors.forename: Cathy
authors.initials: C
authors.lastname: Horvatin
authors.forename: David J T
authors.initials: DJ
authors.lastname: Huang
authors.forename: Kenneth A
authors.initials: KA
authors.lastname: Cornell
authors.forename: Michael K
authors.initials: MK
authors.lastname: Riscoe
authors.forename: P Lynne
authors.initials: PL
authors.lastname: Howell
mesh_terms: D019943:Amino Acid Substitution; D001665:Binding Sites; D002384:Catalysis; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics; D006860:Hydrogen Bonding; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D009699:N-Glycosyl Hydrolases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011487:Protein Conformation; D011683:Purine-Nucleoside Phosphorylase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D055672:Static Electricity
chemical_list: D011683:Purine-Nucleoside Phosphorylase; C021784:5'-methylthioadenosine phosphorylase; D009699:N-Glycosyl Hydrolases; C019606:adenosylhomocysteine nucleosidase