title: Structural and biochemical evidence for a boat-like transition state in beta-mannosidases.
abstract: Enzyme inhibition through mimicry of the transition state is a major area for the design of new therapeutic agents. Emerging evidence suggests that many retaining glycosidases that are active on alpha- or beta-mannosides harness unusual B2,5 (boat) transition states. Here we present the analysis of 25 putative beta-mannosidase inhibitors, whose Ki values range from nanomolar to millimolar, on the Bacteroides thetaiotaomicron beta-mannosidase BtMan2A. B2,5 or closely related conformations were observed for all tightly binding compounds. Subsequent linear free energy relationships that correlate log Ki with log Km/kcat for a series of active center variants highlight aryl-substituted mannoimidazoles as powerful transition state mimics in which the binding energy of the aryl group enhances both binding and the degree of transition state mimicry. Support for a B2,5 transition state during enzymatic beta-mannosidase hydrolysis should also facilitate the design and exploitation of transition state mimics for the inhibition of retaining alpha-mannosidases--an area that is emerging for anticancer therapeutics.
authors.affiliation: Institute for Cell and Molecular Biosciences, The Medical School, Newcastle University, Framlington Place, Newcastle upon Tyne NE2 4HH, UK.
authors.forename: Louise E
authors.initials: LE
authors.lastname: Tailford
authors.forename: Wendy A
authors.initials: WA
authors.lastname: Offen
authors.forename: Nicola L
authors.initials: NL
authors.lastname: Smith
authors.forename: Claire
authors.initials: C
authors.lastname: Dumon
authors.forename: Carl
authors.initials: C
authors.lastname: Morland
authors.forename: Julie
authors.initials: J
authors.lastname: Gratien
authors.forename: Marie-Pierre
authors.initials: MP
authors.lastname: Heck
authors.forename: Robert V
authors.initials: RV
authors.lastname: Stick
authors.forename: Yves
authors.initials: Y
authors.lastname: Blériot
authors.forename: Andrea
authors.initials: A
authors.lastname: Vasella
authors.forename: Harry J
authors.initials: HJ
authors.lastname: Gilbert
authors.forename: Gideon J
authors.initials: GJ
authors.lastname: Davies
mesh_terms: D004791:Enzyme Inhibitors / Q000737:chemistry / Q000494:pharmacology; D006868:Hydrolysis; D018716:Molecular Mimicry; D011487:Protein Conformation; D044902:beta-Mannosidase / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism
chemical_list: D004791:Enzyme Inhibitors; D044902:beta-Mannosidase