THE USE OF NUCLEAR MAGNETIC RESONANCE TO DESCRIBE RELATIVE MODES OF BINDING TO LYSOZYME OF HOMOLOGOUS INHIBITORS AND RELATED SUBSTRATES

Abstract

Proton magnetic resonance has been used to study the association of inhibitors and substrates with hen egg-white lysozyme. Changes in chemical shift, due to association, of acetamido methyl group resonances of the small molecules have been quantitated. This has allowed definition of magnetic parameters for three contiguous binding subsites on the enzyme surface. The relative modes of occupancy of these sites by N-acetyl-D-glucosamine (NAG), chitobiose, chitotriose, their methyl glycosides, and chitotetraose have been delineated. In addition, the binding to these sites of N-acetyl-D-muramic acid (NAM) and a cell-wall disaccharide, NAG-NAM, have been studied. There is good, although not complete, agreement between the results obtained and X-ray analysis studies of the binding of some of these inhibitors to crystalline lysozyme. Binding of synthetic substracts, such as p-nitrophenyl-2-acetamido-4-O-(2-acetamido-2-deoxy-beta-D -glucopyranosyl)-beta-D-glucopyranoside (NAG-Gluc-varphiNO(2)), has also been studied by the magnetic resonance technique described.