Glycophorin amino acid residues

In the spectrum of fully reductively [ C] methylated glycophorin A, the resonance at 42.8 p.p.m. must correspond to the N, N -di[ C]methylated, N-terminal amino acid residue. The ratio of the integrated intensities of the N, N -di[ C]methylLeu resonance to the N, N -di[ C]methyllysine resonances is 5 1, as expected. The integration values determined were valid, because the recycle times of spectra in Figs. 3B, 3C, and 3D were twice the spin-lattice relaxation-times (Tj values) of those of the di[ C]methyl carbon atoms, and also because the n.O.e. values of the N, N -di[ C]methyl and N, N -di[ C]methyl carbon atoms were equivalent. ... 

The results concerning the N-terminal structures of glycophorins A" and A were based on the labels that were placed on the crucial, N-terminal amino group, and they clearly showed that the amino acid residues at position S may play only a minor, if any, role in determining the structure of the MN blood-group determinants. The carbohydrate residues appear... 

As mentioned earlier, glycophorin B carries the N and the Ss blood-group antigens. It is known that the first 26 residues of the amino acid sequence are identical to those in the N-terminal portion of glycophorin A". Moreover, relative to glycophorin A, it has a shortened amino acid chain, comprising 35 amino acid residues at the C-terminus. It is also known to contain 4 lysine residues. 

The possible role that the lysine residues, N-terminal amino acid residues, and carbohydrate residues may play in the display of the MN blood-group determinants by glycophorins A, A, and has been investigated. Assuming that the N-terminal amino acid in each of these glycoproteins plays a prominent role in the display of the MN blood-group determinant, labels were placed on the N-terminal amino acid residues of the glycoproteins. 

It is now well established that the MN blood-group antigens are situated99-101 on the major sialoglycoprotein (glycophorin A) of the erythrocyte membrane. The complex, antigenic structure resides within the first five amino acid residues from the N-terminal portion of the molecule three of these residues are glycosylated. 

Topography of glycophorin in the mammalian erythrocyte membrane. Carbohydrate residues (small blue hexagons) are attached to the hydroxyl groups of threonine and serine residues in the N-terminal domain of the protein. The N-terminus and all of the carbohydrates are outside the cell the C-terminal domain of the protein is inside. The hydrophobic, membrane-spanning domain is flanked by charged amino acid residues that may interact electrostatically with the polar head-groups of the phospholipids. 

Glycophorin A is a glycoprotein that extends across the red blood cell membrane. The portion of the polypeptide that extends across the membrane bilayer contains 19 amino acid residues and is folded into an a helix. What is the -width of the bilayer that could be spanned by this helix The interior of the bilayer includes long acyl chains that are nonpolar. Which of the 20 L amino acids would you expect to find among those in the portion of the polypeptide that traverses the bilayer ... 

Within this membrane structure sit protein molecules, in about equal weight to the lipids, and these cannot be readily removed because they are anchored by ten or twenty hydrophobic amino acids.For example, a red blood cell membrane contains largely glycophorin molecules which have 131 amino acid residues and about 100 saccharide residues arranged as 16 short carbohydrate chains about 1 nm long. ... 

The amino acid sequences for glycophorins A and A (see Refs. 8 and 19) are presented in Fig. 1. It may be clearly seen that residues 1-70 of these glycoproteins extend into the cell exterior. The hydrophobic portion of the glycoprotein, residues 71-92, appear to be imbedded in the phospholipid membrane, and residues 93-131 protrude into the cell cytoplasm. ... 

After the introduction of C-labels into the protein or glycoprotein molecule, the ability to assign the resonances to specific carbon atoms is essential. In the case of glycophorin (see Fig. 1), it may readily be seen that 5 lysine residues and 1 N-terminal amino acid (per species) can be reduc-tively di[ C]methylated. This could theoretically lead to 6 resonances (or possibly more, if chemical-shift nonequivalence is observed for the dimethyl species) in the C spectrum of methylated glycophorin A. However, in most cases, the N, N -di[ C]methyllysine resonances all occur near, or at, the same frequency. It is then necessary to be able at least to assign, or... 

Carbon-13 Assignments for the Amino Acid and Carbohydrate Residues of TrrGlycopeptide of Human Glycophorin AM and Related Compounds"... 

Figure 12.27 Locating the membrane-spanning helix of glycophorin. (A) Amino acid sequence and transmembrane disposition of glycophorin A from the red-blood-celI membrane. Fifteer) O-linked carbohydrate units are shown as diamond shapes, and an N-linked unit is shown as a lozenge shape. The hydrophobic residues (yellow) buried in the bilayer form a transmembrane a helix. The carboxyl-terminal part of the molecule, located on the cytoplasmic ydeof the membrane, is rich in negatively charged (red) and positively charged (blue) residues,...

Although glycophorin B contains the same O-linked oligosaccharides as glycophorin A, EBA-175 did not bind to it. Later, the reason for this would be shown to be that the binding of EBA-175 to glycophorin A is not solely determined by sialic acid residues but also requires specific amino acid sequences (Sim et ah, 1994). 

---