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Publication Abstract from PubMed

The understanding of features that determine transglycosylation (TG) activity in glycoside hydrolases is important because it would allow the construction of enzymes that can catalyze controlled synthesis of oligosaccharides. To increase TG activity in two family 18 chitinases, chitinase D from Serratia proteamaculans (SpChiD) and chitinase A from Serratia marcescens (SmChiA), we have mutated residues important for stabilizing the reaction intermediate and substrate binding in both donor and acceptor sites. To help mutant design, the crystal structure of the inactive SpChiD-E153Q mutant in complex with chitobiose was determined. We identified three mutations with a beneficial effect on TG activity: Y28A (affecting the -1 subsite and the intermediate), Y222A (affecting the intermediate) and Y226W (affecting the +2 subsite). Furthermore, exchange of D151, the middle residue in the catalytically important DXDXE motif, to asparagine, reduced hydrolytic activity up to 99 % with a concomitant increase of apparent TG activity. The combination of mutations yielded even higher degrees of TG activity. Reactions with the best mutant, SpChiD-D151N/Y226W/Y222A, led to rapid accumulation of high levels of TG products that remained stable over time. Importantly, the introduction of analogous mutations at same positions in SmChiA (Y163A equal to Y28A and Y390F similar to Y22A) had similar effects on TG efficiency. Thus, the combination of reducing hydrolytic power, subsite affinity and the stability of intermediate states provides a powerful, general strategy for creating hypertransglycosylating mutants of retaining glycoside hydrolases.

Key residues affecting transglycosylation activity in family 18 chitinases - Insights into donor and acceptor subsites.,Madhuprakash J, Dalhus B, Rani TS, Podile AR, Eijsink VGH, Sorlie M Biochemistry. 2018 Jun 25. doi: 10.1021/acs.biochem.8b00381. PMID:29939724^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.