Withers, Stephen

A compelling experiment tipped the scales decidedly in favor of the SN2 pathway, as reported by Stephen Withers and colleagues in 2001. Making use of a mutant enzyme (with residue 35 changed from Glu to Gin) and artificial substrates, which combined to slow the rate of key steps in the reaction, these workers were able to stabilize the elusive covalent intermediate. This in turn allowed them to observe the intermediate directly, using both mass spectrometry and x-ray crystallography (Fig. 6-25b). 

Stephen G. Withers (Canada) Enzymatic cleavage and formation of glycosidic bonds from glycosidases and lyases to transferases and glycosynthases 2004—Made jointly to Anne Imberty (France) and Thomas Peters (Germany) Forty ways to bind your sugar ... 

Fluorodeoxy glucose compounds and C labeled sugars were purchased through Sigma chemical company. Fluorodeoxy galactose compounds were a generous gift from Dr. Stephen Withers, University of British Columbia. 

Ran Zhang, Vivian L. Y. Yip, and Stephen G. Withers, University of British Columbia, Vancouver, BC, Canada... 

Ran Zhang was born in Jiangsu Province, China. He received his B.Sc. from Peking University, P. R. China while working in the laboratory of Professor Zhongfan Liu. In 2004 he joined Professor Stephen G. Withers group at the University of British Columbia as a Ph.D. candidate. His research focuses on the mechanistic studies of ct-glycosidases and is funded by the British Columbia Innovation Council. 

Vivian L. Y. Yip received her undergraduate and graduate training at the University of British Columbia. She completed her B.Sc. degree in 2002 and her Ph.D. under the supervision of Dr. Stephen G. Withers in 2007. Her graduate work focused on the mechanistic elucidation of unusual glycosidases. She was funded by NSERC and the Michael Smith Foundation for Health Research during this time. She is also the recipient of the CCUCC Chemistry Doctoral Award. 

Stephen G. Withers (B.Sc. and Ph.D.) was trained at the University of Bristol, UK, where he obtained his Ph.D. under the supervision of Dr. Michael Sinnott. Later he moved to Canada as a postdoctoral fellow, applying heteronuclear NMR to the study of enzymatic catalysis with Drs. Brian Sykes and Neil Madsen in the Department of Biochemistry at the University of Alberta. In 1982 he moved to the University of British Columbia as assistant professor of chemistry. He now holds the Khorana Chair of Chemistry and Biochemistry at UBC and serves as the director of CHiBi, the Centre for High-throughput Biology at UBC. 

Strong evidence from mass spectrometry su ests that the mechanism of lysozyme involves sequential 5 2 reactions and a covalent enzyme—substrate intermediate (based on work by Stephen Withers and colleagues at the University of British Columbia and elsewhere). Asp-52 acts as the nucleophile in the first step, covalently bonding the substrate to the enzyme. A water molecule acts as a nucleophile in the second step to complete the formation of product and free the substrate from the active site. In both steps, Glu-35 serves as a general acid—base catalyst. The details are as follows. 

Stephen G. Withers Department of Chemistry University of British Columbia 2036 Main Mall Vancouver, B.C. V6T IZl Canada... 

Susan M Hancock, Jamie R Rich, Matthew E C Caines, Natalie CJ Strynadka Stephen G Withers... 

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