13C-N.M.R.-spectral study of the pH behavior of reductively [13C]methylated, glycophorin a glyco-octapeptides and a related glycopentapeptide

Possible role of the carbohydrate residues on the structure of the N-terminus of glycophorin AM

Natural-abundance 13C nuclear magnetic resonance (13C-n.m.r.) was used to study the effect of monoglycosylation on the structure and dynamics of a pentapeptide related to the N-terminus of glycophorin AM. The results of this study indicate that a single point of glycosylation, on the pentapeptide, can significantly affect its structure. Moreover, glycosylation of this pentapeptide also affects its dynamic motion in solution. This study further defines the role that the carbohydrate residue plays in determining the structure about the N-terminus of glycophorin AM.

Structural, dynamic, and metal-ion binding studies of the core glycopeptides beta-D-Gal-(1----3)-alpha-D-GalNAc----Ser, Thr by 13C-N.m.r. spectroscopy

13C-N.m.r. spectral data as well as spin-lattice relaxation times (T1 values) are presented for the core glycopeptides beta-D-Gal-(1----3)-alpha-D-GalNAc----Ser, Thr. The binding of Gd3+ to these model compounds containing N-terminal blocking groups and esterified carboxyl groups indicates that the disaccharide contains a rather weak, but unique, binding-site in the vicinity of C-2 of alpha-D-GalNAc (possibly involving N-2', the acetamido carbonyl group, O-3' and/or possibly the glycosidic oxygen atom (O-3)).

A 13C-methylation study of glycophorin A intact erythrocytes by 13C-NMR spectroscopy

N-terminal N alpha-[13C]monomethylamino derivatives for the N-terminal serine and leucine residues of glycophorins AM and AN, respectively, were obtained by reductively 13C-methylating homozygous human erythrocytes (MM, NN). The 13C-labeled glycophorins, AM and AN, were then isolated. A unique structural state was observed in solution reductively 13C-methylated glycophorin AM that was not observed in glycophorin AM derived from 13C-methylated erythrocytes. We attribute this state to the fact that some of the glycophorin AM forms a head-to-head dimer when subjected to reductive 13 C-methylation in aqueous solution. The 13C chemical shift data and pH titration data for the N-terminal [13C]dimethylamino and [13C]monomethylamino groups of glycophorin AM and AN derived from reductively 13C-methylated erythrocytes were in agreement with the chemical shift and titration data previously obtained for the N-terminal [13C]dimethylamino groups of solution reductively 13C-methylated glycophorins and related glycopeptides and peptides and N-terminal [13C]monomethylamino groups of related glycopeptides and peptides.

13C-NMR spectral study of reductively [13C]methylated glycophorin B

Glycophorin BN was reductively [13C]methylated and the 13C chemical shift of the N-terminal [13C]dimethyl-leucine residue was monitored as a function of pH. These results were compared to the pH-dependent chemical shift studies of the N-terminal [13C]dimethylleucine residues of intact glycophorin AN and N-terminal glyco-octapeptide AN. The results indicate that the titration data for [13C]dimethylleucine of glycophorin BN more closely resembles the titration data observed for the [13C]dimethylleucine residue of the N-terminal glyco-octapeptide AN rather than for the [13C]dimethylleucine residue of intact glycophorin AN. Integration of the 13C resonances indicated that glycophorin BN contains 3-4 lysine residues.