71693-36-2Relevant academic research and scientific papers
Probing synergy between two catalytic strategies in the glycoside hydrolase O-GlcNAcase using multiple linear free energy relationships
Greig, Ian R.,Macauley, Matthew S.,Williams, Ian H.,Vocadlo, David J.
supporting information; experimental part, p. 13415 - 13422 (2010/01/16)
Human O-GlcNAcase plays an important role in regulating the post-translational modification of serine and threonine residues with β-O-linked N-acetylglucosamine monosaccharide unit (O-GlcNAc). The mechanism of O-GlcNAcase involves nucleophilic participation of the 2-acetamido group of the substrate to displace a glycosidically linked leaving group. The tolerance of this enzyme for variation in substrate structure has enabled us to characterize O-GlcNAcase transition states using several series of substrates to generate multiple simultaneous free-energy relationships. Patterns revealing changes in mechanism, transition state, and rate-determining step upon concomitant variation of both nucleophilic strength and leaving group abilities are observed. The observed changes in mechanism reflect the roles played by the enzymic general acid and the catalytic nucleophile. Significantly, these results illustrate how the enzyme synergistically harnesses both modes of catalysis; a feature that eludes many small molecule models of catalysis. These studies also suggest the kinetic significance of an oxocarbenium ion intermediate in the O-GlcNAcase-catalyzed hydrolysis of glucosaminides, probing the limits of what may be learned using nonatomistic investigations of enzymic transition-state structure and offering general insights into how the superfamily of retaining glycoside hydrolases act as efficient catalysts.
O-GlcNAcase catalyzes cleavage of thioglycosides without general acid catalysis
Macauley, Matthew S.,Stubbs, Keith A.,Vocadlo, David J.
, p. 17202 - 17203 (2007/10/03)
O-GlcNAcase catalyzes the removal of N-acetylglucosamine residues from serine and threonine residues of post-translationally modified proteins using a catalytic mechanism involving substrate-assisted catalysis and general acid/base catalysis. Since thioglycosides are widely perceived as resistant to hydrolysis by glycosidases, it was surprising to find that O-GlcNAcase also catalyzes the efficient hydrolysis of S-glycosides. Bronsted analyses and pH-activity studies of the O-GlcNAcase-catalyzed hydrolysis of a series of aryl S- and O-glycosides reveal that O-GlcNAcase effects hydrolysis of thioglycosides without the assistance of general acid catalysis. α-Deuterium kinetic isotope effects for O- and S-glycosides, as well as Taft-like analyses using N-fluoroacetyl-β-glycosides, suggest that O-GlcNAcase accomplishes hydrolysis of thioglycosides by stabilizing late transition states. For S-glycosides this transition state shows greater nucleophilic participation from the 2-acetamido group than for O-glycosides. The rate constants governing the O-GlcNAcase-catalyzed hydrolysis of O- and S-glycosides as compared to those previously determined for the spontaneous hydrolysis of structurally similar O,O- and O,S-acetals show a similar ratio. O-GlcNAcase therefore demonstrates similar catalytic proficiency toward both O- and S-glycosides. We conclude that O-GlcNAcase is a bifunctional catalyst capable of efficiently cleaving thioglycosides without general acid catalysis, an observation that may have biological implications. Copyright
