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Cover Picture: Enzymatic Thioxyloside Synthesis: Characterization of Thioglycoligase Variants Identified from A Site-Saturation Mutagenesis Library of Bacillus Circulans Xylanase (ChemBioChem 4/2010)
The cover picture shows the reaction intermediate formed at the active site of a mutant of the Bacillus circulans xylanase that has been optimized for the synthesis of thioglycoside products. Saturation mutagenesis of the codon corresponding to its catalytic acid/base residue generated a library of transformants. Screening of crude cell extracts in situ for activity by TLC analysis and for protein concentration by active-site titration identified the best mutants without the need for purification. The thioglycoside products are resistant to enzymatic degradation, thus they serve as inhibitors of the wild-type enzyme for structural studies. For more information, see the paper by S. G. Withers et al. on p. 533 ff.