title: Structural insights into the reaction mechanism of S-adenosyl-L-homocysteine hydrolase.
abstract: S-adenosyl-L-homocysteine hydrolase (SAH hydrolase or SAHH) is a highly conserved enzyme that catalyses the reversible hydrolysis of SAH to L-homocysteine (HCY) and adenosine (ADO). High-resolution crystal structures have been reported for bacterial and plant SAHHs, but not mammalian SAHHs. Here, we report the first high-resolution crystal structure of mammalian SAHH (mouse SAHH) in complex with a reaction product (ADO) and with two reaction intermediate analogues-3'-keto-aristeromycin (3KA) and noraristeromycin (NRN)-at resolutions of 1.55, 1.55, and 1.65 Å. Each of the three structures constitutes a structural snapshot of one of the last three steps of the five-step process of SAH hydrolysis by SAHH. In the NRN complex, a water molecule, which is an essential substrate for ADO formation, is structurally identified for the first time as the candidate donor in a Michael addition by SAHH to the 3'-keto-4',5'-didehydroadenosine reaction intermediate. The presence of the water molecule is consistent with the reaction mechanism proposed by Palmer &Abeles in 1979. These results provide insights into the reaction mechanism of the SAHH enzyme.
authors.affiliation: School of Pharmacy, Showa University, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan.
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Kusakabe
authors.affiliation: School of Pharmacy, Showa University, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan.
authors.forename: Masaaki
authors.initials: M
authors.lastname: Ishihara
authors.affiliation: School of Pharmacy, Showa University, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan.
authors.forename: Tomonobu
authors.initials: T
authors.lastname: Umeda
authors.affiliation: School of Pharmacy, Showa University, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Kuroda
authors.affiliation: College of Pharmaceutical Sciences, Matsuyama University, 4-2 Bunkyo-cho, Matsuyama, Ehime 790-8578, Japan.
authors.forename: Masayuki
authors.initials: M
authors.lastname: Nakanishi
authors.affiliation: Faculty of Engineering, Gifu University, 1-1 Yanagido, Gifu, Gifu 501-1193, Japan.
authors.forename: Yukio
authors.initials: Y
authors.lastname: Kitade
authors.affiliation: School of Pharmacy, Showa University, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Gouda
authors.affiliation: School of Pharmacy, Showa University, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan.
authors.forename: Kazuo T
authors.initials: KT
authors.lastname: Nakamura
authors.affiliation: School of Pharmacy, Showa University, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan.
authors.forename: Nobutada
authors.initials: N
authors.lastname: Tanaka
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives / Q000737:chemistry / Q000378:metabolism; D043383:Adenosylhomocysteinase / Q000737:chemistry* / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D055162:Biocatalysis; D018360:Crystallography, X-Ray; D006868:Hydrolysis; D051379:Mice; D056004:Molecular Dynamics Simulation; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D012435:S-Adenosylhomocysteine / Q000378:metabolism; D016415:Sequence Alignment; D013379:Substrate Specificity
chemical_list: C030034:aristeromycin; D012435:S-Adenosylhomocysteine; D043383:Adenosylhomocysteinase; D000241:Adenosine