Structural and biochemical evidence for a boat-like transition state in beta-mannosidases.
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.
Tailford
Louise E
LE
Institute for Cell and Molecular Biosciences, The Medical School, Newcastle University, Framlington Place, Newcastle upon Tyne NE2 4HH, UK.
Offen
Wendy A
WA
Smith
Nicola L
NL
Dumon
Claire
C
Morland
Carl
C
Gratien
Julie
J
Heck
Marie-Pierre
MP
Stick
Robert V
RV
Blériot
Yves
Y
Vasella
Andrea
A
Gilbert
Harry J
HJ
Davies
Gideon J
GJ
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
D004791:Enzyme Inhibitors; D044902:beta-Mannosidase