H-1-NUCLEAR-MAGNETIC-RESONANCE STUDIES ON GLYCOPHORIN AND ITS CARBOHYDRATE-CONTAINING TRYPTIC PEPTIDES

The (1H) NMR spectra of [human] glycophorin and its tryptic sialoglycopeptides were investigated. The intensities of the assigned resonances indicated that all of the residues in the sialoglycopeptides are sufficiently mobile in conformation to give sharp resonances, while in glycophorin this was true for only approximately 80% of the peptide backbone. The resonances of the central sequence of some 20 of the hydrophobic residues were strongly broadened. This region was probably that of .alpha.-helical structure which aggregates. The linewidths and intensities of the resonances were not, or only slightly, affected by changing the ionic strength, temperature or by carboxymethylation of the Met-81 residue in glycophorin. Glycophorin bound about 100 mol sodium dodecylsulfate [SOS]/mol protein as derived from studies on linebroadening of the latter''s C-3 to C-11 methylene resonances. The bound SDS probably increased the mobilities of the hydrophobic residues in the protein as these resonance intensities were increased by the binding. The carbohydrate chains in glycophorin were conformationally mobile; no evidence was found for tight carbohydrate-protein interactions. The relevance of flexible carbohydrate chains in membrane glycoproteins was discussed in relation to cell surface chemistry.