INTERACTIONS OF 3-DEOXY AND 6-DEOXY DERIVATIVES OF N-ACETYL-D-GLUCOSAMINE WITH HEN LYSOZYME

The interactions of deoxy derivatives of GlcNAc [N-acetyl-D-glucosamine], 6-deoxy-GlcNAc and 3-deoxy-GlcNAc with hen egg-white lysozyme [EC 3.2.1.17] were studied at various pH by measuring the changes in the circular dichroic (CD) band at 295 nm. 6-Deoxy-GlcNAc and 3-deoxy-GlcNAc bind at subsite C of lysozyme and compete with GlcNAc. The pH dependence of the binding constant of 6-deoxy-GlcNAc was the same as that of GlcNAc, but the binding constants of 3-deoxy-GlcNAc were 3-10 times smaller than those of GlcNAc in the pH range from 3-9. X-ray crystallographic studies show that O(6) and O(3) of GlcNAc at subsite C are H-bonded to the indole NH of Trp 62 and Trp 63, respectively, but the above results indicate that Trp 63, not Trp 62, is important for the interaction of GlcNAc with lysozyme.