Hexasaccharide binding sites

Fig. 5. The binding sites for the hexasaccharide to lysozyme, indicating residues implicated in the catalytic cleavage.

The structure of the complex formed between the enzyme lysozyme and its substrate. The crevice that forms the site for substrate binding (the active site) runs horizontally across the enzyme molecule. The individual hexose sugars of the hexasaccharide substrate are shown in a darker color and labeled A-F. (Coordinates courtesy of D. C. Philips, Oxford, England.) (Illustration copyright by Irving Geis. Reprinted by permission.)... 

The hexasaccharide (NAG—NAM)s—(NAG)a was also found to bind on the left side of the cleft. In contrast, the alternating copolymer (NAG—NAM)s was bound with its F-site residue on the right side, residues such as Phe-34 and Arg-114 being involved (the lacteal side chain of NAM prevents F-site binding on the left side). 

Fig. 4.5. Structure of an hexasaccharide that can bind at the active center of lysozyme. Upon binding to the enzyme, the sugar ring D of the substrate becomes distorted and catalysis proceeds through the promotion of an oxocarbonium ion (see p. 228). This results in a polar transition state. However, an important feature of enzyme is the capacity to stabilize (neutralize) the enzyme-substrate complex by electrostatic interactions with amino acid residues at the active site.

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