Crystal structures of egg-white lysozyme of hen in acetate-free medium and of lysozyme complexes with N-acetylglucosamine and beta-methyl N-acetylglucosaminide.

The binding of beta-methyl N-acetylglucosaminide (betaMeGlcNAc) to egg-white lysozyme of hen in the tetragonal crystal form was studied by X-ray diffraction techniques to a resolution of 0.25 nm. The binding of the beta-methyl glycoside is almost identical with the binding of beta-N-acetylglucosamine (betaGlcNAc). Real-space refinement of the lysozyme-alpha/beta GlcNAc and lysozyme-betaMeGlcNAc complexes allowed preliminary analysis of the conformational changes observed on binding monosaccharide inhibitors, specially in the region involving tryptophan-62 and residues 70--76. Tetagonal lysozyme crystals, grown in the absence of acetate ions, were examined by X-ray diffraction to 0.25nm resolution. The resulting difference Fourier synthesis shows no firm evidence for bound acetate ions and indicates only minor conformational changes in the side-chain positions of aspartic acid-101 and asparagine-103. The close similarity of the lysozyme structures in the presence and absence of acetate is contrary to expectations from previous n.m.r. studies.