Isolation of glycophorin with deoxycholate.

In a previous communication we reported that human erythrocyte glycophorin prepared by the lithium diiodosalicylate phenol procedure contains approximately 10 mol of lithium diiodosalicylate per mol of glycophorin, and further we showed that this bound lithium diiodosalicylate is difficult to remove by detergents or organic solvents (Romans, A.Y. and Segrest, J.P. (1978) Biochim. Biophys. Acta 511, 297-301). In the present communication we report an alternative purification procedure for glycophorin in which sodium deoxycholate is substituted for lithium diiodosalicylate; the sodium deoxycholate is subsequently removed by gel filtration. Utilizing this procedure, 25-30 mg glycophorin are obtained per gram of lyophilized erythrocyte ghosts. The glycophorin prepared by the sodium deoxycholate procedure, after a single gel filtration step, contains less than 1 mol of sodium deoxycholate per mol glycophorin and is colorless compared with glycophorin prepared by the lithium diiodosalicylate procedure, which has a distint reddish-brown cast.     

Isolation of glycophorin with deoxycholate

In a previous communication we reported that human erythrocyte glycophorin prepared by the lithium diiodosalicylate phenol procedure contains approximately 10 mol of lithium diiodosalicylate per mol of glycophorin, and further we showed that this bound lithium diiodosalicylate is difficult to remove by detergents or organic solvents (Romans, A.Y. and Segrest, J.P. (1978) Biochim. Biophys. Acta 511, 297–301). In the present communication we report an alternative purification procedure for glycophorin in which sodium deoxycholate is substituted for lithium diiodosalicylate; the sodium deoxycholate is subsequently removed by gel filtration. Utilizing this procedure, 25–30 mg glycophorin are obtained per gram of lyophilized erythrocyte ghosts. The glycophorin prepared by the sodium deoxycholate procedure, after a single gel filtration step, contains less than 1 mol of sodium deoxycholate per mol glycophorin and is colorless compared with glycophorin prepared by the lithium diiodosalicylate procedure, which has a distinct reddish-brown cast.     

Amino acid sequence and oligosaccharide attachment sites of the glycosylated domain of dog erythrocyte glycophorin

Glycophorin was prepared from dog erythrocyte membranes by extraction with lithium diiodosalicylate and partition in aqueous phenol. Tryptic and chymotryptic treatments of the glycophorin produced two major glycopeptides labeled T1 and CH1, respectively. The glycopeptides were isolated by gel chromatography followed by ion-exchange chromatography, and subjected to amino acid sequence analysis. Both glycopeptides represented the amino-terminal domain of the major dog glycophorin; T1 of 52 residues and CH1 of 43 residues. The amino-terminal sequence of dog glycophorin does not have significant homology with those of human, horse or porcine glycophorins. This result is in good agreement with our previous proposal that there is no homology in the sequence of the amino-terminal glycosylated domain of glycophorin.     

Isolation of the major intrinsic transmembrane protein of the human erythrocyte membrane.

The major intrinsic protein of the human erythrocyte membrane commonly referred to as "Band 3", was isolated by a multi-step procedure. Extraction of ghost membranes in dilute solutions of lithium diiodosalicylate removed most of the proteins considered to be extrinsic to the membrane. The resulting membrane fragments were solubilized in sodium dodecyl sulfate, and the major sialoglycoprotein (glycophorin A) was removed by wheat germ agglutinin-Sepharose affinity chromatography. Gel filtration in sodium dodecyl sulfate was used as the final step to yield the band 3 polypeptide in electrophoretically homogeneous form.     

Structural changes in alkaline-treated postsynaptic membranes from Torpedo marmorata are not due to lipid hydrolysis

The removal of the 43 kDa peptide from postsynaptic membranes from the electric organ of Torpedo by alkaline treatment (pH 11) or by lithium diiodosalicylate at pH 8 results in similar ultrastructural changes that cannot be produced by the action of porcine pancreatic phospholipase A₂ or lysophosphatidylcholine. Thin-layer chromatography fails to reveal significant alkaline hydrolysis of membrane lipids from postsynaptic membranes and erythrocyte ghosts under the conditions used for peptide extraction.     

Rat erythrocyte glycophorins can be isolated by the lithium diiodosalicylate method used for other glycophorins.

1. The lithium diiodosalicylate/phenol method, widely employed for the isolation of membrane sialoglycoproteins (glycophorins) from mammalian erythrocytes, was applied for the first time to the purification of homologous glycoproteins from rat erythrocyte membranes. 2. The resulting preparations showed to be composed of four components, fractionated on SDS-PAGE. All four were positive for periodic acid-Schiff's reagent stain, the two largest of them being major. 3. Isolated rat glycophorins accounted for 60% of the ghost sialic acid and 1.5% of their protein. The presence of O-acetyl groups was confirmed in one-third of the sialic acid residues. 4. The molecular masses of the four glycophorin components were determined by a method which takes into account the anomalous mobility of glycoproteins on SDS-electrophoresis. Estimated values thus obtained for the actual molecular masses were 74, 32, 25 and 17 kDa.     

Isolation of the major intrinsic transmembrane protein of the human erythrocyte membrane

Summary The major intrinsic protein of the human erythrocyte membrane commonly referred to as Band 3, was isolated by a multi-step procedure. Extraction of ghost membranes in dilute solutions of lithium diiodosalicylate removed most of the proteins considered to be extrinsic to the membrane. The resulting membrane fragments were solubilized in sodium dodecyl sulfate, and the major sialoglycoprotein (glycophorin A) was removed by wheat germ agglutinin-Sepharose affinity chromatography. Gel filtration in sodium dodecyl sulfate was used as the final step to yield the band 3 polypeptide in electrophoretically homogeneous form.     

Isolation of human platelet glycoproteins.

Human platelet glycoproteins were isolated from whole platelets by two methods. The first method, that of affinity chromatography on wheat germ agglutinin, is based on the known affinity of lectins for cell surface glycoproteins. When solubilized whole platelets are used as starting material for this procedure, elution with N-acetylglucosamine yields primarily a glycoprotein of Mr approximately 150 000 as estimated by sodium dodecyl sulfate-acrylamide gel electrophoresis. The second method is based on the ability of the chaotropic salt lithium diiodosalicylate to extract glycoprotein from particulate cell fractions in water-soluble form. This method yields three major glycopeptides with apparent molecular weights after sulfhydryl reduction of 145 000, 125 000, and 95 000 as estimated on 5.6% sodium dodecyl sulfate-acrylamide gels. Carboxymethylation of these preparations in the presence of sulfhydryl-reducing agent further resolves a glycoprotein of Mr approximately 165 000. Treatment of whole platelets by periodate oxidation and sodium[3H]-borohydride reduction labels the three major glycoproteins extracted by lithium diiodosalicylate and the glycoprotein of Mr approximately 150 000 isolated on wheat germ agglutinin confirming their surface orientation. However, glycoprotein with Mr approximately 165 000 resolved by carboxymethylation of the lithium diiodosalicylate extracted glycoprotein mixture was not labelled by this method, suggesting that it represents the granule protein with similar electrophoretic characteristics described by others. Phosphorylation of intact platelets with 32Pi also results in labelling of glycoproteins isolated by both methods, suggesting that these molecules traverse the bilipid layer of the platelet membrane, bearing reactive groups on both outer and cytoplasmic surfaces.     

1H-Nuclear magnetic-resonance studies on glycophorin and its carbohydrate-containing tryptic peptides.

The proton nuclear magnetic resonance (1H-NMR) spectra of glycophorin and its tryptic sialoglycopeptides were investigated. From the intensities of the assigned resonances it was concluded that all of the residues in the sialoglycopeptides are sufficiently mobile in conformation to give sharp resonances, while in glycophorin this is true for only approximately 80% of the peptide backbone. The resonances of the central sequence of some 20 of the hydrophobic residues are strongly broadened. This region is probably that of alpha-helical structure which is known to aggregate. The linewidths and intensities of the resonances are not, or only slightly, affected by changing the ionic strength, temperature or by carboxymethylation of the Met-81 residue in glycophorin. Glycophorin was found to bind about 100 mol sodium dodecylsulphate/mol protein as derived from studies on linebroadening of the latter's C-3 to C-11 methylene resonances. The bound dodecyl-sulphate probably increases the mobilities of the hydrophobic residues in the protein as these resonance intensities are 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 is discussed in relation to cell surface chemistry.     

Abnormal membrane protein methylation and merocyanine 540 fluorescence in sickle erythrocyte membranes

Sickle cell erythrocytes exhibit reduced carboxyl methylation of membrane proteins compared to normal erythrocytes. This altered methylation in sickle membrane proteins is also observable when extracted membranes, both intact and alkali treated, were used as substrates for the homologous protein methylase II (S-adenosylmethionine:protein-carboxyl O-methyltransferase, EC. 2.1.1.24). However, when glycophorin A, one of the major methyl acceptors in both membranes, was extracted by lithium diiodosalicylate and used as the methyl acceptor, the proteins from both membranes were methylated equally, suggesting an involvement of membrane structure in membrane-bound protein methylation. Merocyanine 540 (MC-540), a fluorescent probe, was used to determine if the membranes differed in organization. Incubation of both normal and sickle erythrocytes membranes with MC-540 produced a marked increase in extrinsic fluorescence, reflecting a relatively nonpolar environment for the dye bound to the membranes. The fluorescence from sickle cell ghosts was only 87% as intense as that from normal ghosts, while the actual amount of MC-540 associated with sickle cell membranes was only 62% of normal. These data suggest that differences exist in the distribution of surface charges on these plasma membranes. These results are consistent with the hypothesis that abnormal levels of membrane protein methylation observed in sickle erythrocytes may be a result of abnormal membrane organization characteristic to sickle cell anemia.     

Reconstitution of mating active membrane vesicles in Paramecium

Mating-active membrane vesicles isolated from cilia of Paramecium caudatum by the urea-EDTA method were dissolved in 9 mM lithium diiodosalicylate (LIS). Membrane vesicles were reconstituted from the LIS-soluble fraction by dialysis. They showed an ability to induce conjugating pairs without prior occurrence of mating agglutination. The same kind of membrane vesicles was obtained when cilia were treated with 4 mM LIS and stored after removing LIS for two weeks.     

Sequence context modulates the stability of a GxxxG-mediated transmembrane helix-helix dimer

To quantify the relationship between sequence and transmembrane dimer stability, a systematic mutagenesis and thermodynamic study of the protein-protein interaction residues in the glycophorin A transmembrane helix-helix dimer was carried out. The results demonstrate that the glycophorin A transmembrane sequence dimerizes when its GxxxG motif is abolished by mutation to large aliphatic residues, suggesting that the sequence encodes an intrinsic propensity to self-associate independent of a GxxxG motif. In the presence of an intact GxxxG motif, the glycophorin A dimer stability can be modulated over a span of -0.5 kcal mol(-1) to +3.2 kcal mol(-1) by mutating the surrounding sequence context. Thus, these flanking residues play an active role in determining the transmembrane dimer stability. To assess the structural consequences of the thermodynamic effects of mutations, molecular models of mutant transmembrane domains were constructed, and a structure-based parameterization of the free energy change due to mutation was carried out. The changes in association free energy for glycophorin A mutants can be explained primarily by changes in packing interactions at the protein-protein interface. The energy cost of removing favorable van der Waals interactions was found to be 0.039 kcal mol(-1) per A2 of favorable occluded surface area. The value corresponds well with estimates for mutations in bacteriorhodopsin as well as for those mutations in the interiors of soluble proteins that create packing defects.     

Coisolation of glycophorin A and polyphosphoinositides from human erythrocyte membranes.

The lipid composition of purified erythrocyte membrane glycophorin was measured. Diphosphoinositide, triphosphoinositide, and phosphatidylserine are the major phospholipids in glycophorin preparation. Nearly all of the radioactive diphosphoinositide and triphosphoinositide extracted from erythrocyte membranes by lithium d?odosalicylate are recoverd in purified glycophorin. There appeared to be no significant enrichment of other acidic membrane phospholipids in the protein. The results do not permit a firm conclusion as to whether the polyphosphoinositides are associated specifically with the membrane protein or whether fortuitous binding has occurred during purification.     

Isolation of human platelet glycoproteins

Human platelet glycoproteins were isolated from whole platelets by two methods. The first method, that of affinity chromatography on wheat germ agglutinin, is based on the known affinity of lectins for cell surface glycoproteins. When solubilized whole platelets are used as starting material for this procedure, elution with N-acetylglucosamine yields primarily a glycoprotein of M_r ≈ 150 000 as estimated by sodium dodecyl sulfate-acrylamide gel electrophoresis. The second method is based on the ability of the chaotropic salt lithium diiodosalicylate to extract glycoprotein from particulate cell fractions in water-soluble form. This method yields three major glycopeptides with apparent molecular weights after sulfhydryl reduction of 145 000, 125 000, and 95 000 as estimated on 5.6% sodium dodecyl sulfate-acrylamide gels. Carboxymethylation of these preparations in the presence of sulfhydryl-reducing agent further resolves a glycoprotein of M_r ≈ 165 000.Treatment of whole platelets by periodate oxidation and sodium[³H]borohydride reduction labels the three major glycoproteins extracted by lithium diiodosalicylate and the glycoprotein of M_r ≈ 150 000 isolated on wheat germ agglutinin confirming their surface orientation. However, glycoprotein with M_r ≈ 165 000 resolved by carboxymethylation of the lithium diiodosalicylate extracted glycoprotein mixture was not labelled by this method, suggesting that it represents the granule protein with similar electrophoretic characteristics described by others.Phosphorylation of intact platelets with ³²P_i also results in labelling of glycoproteins isolated by both methods, suggesting that these molecules traverse the     

Peptide heterogeneity in the band 3 protein of rabbit erythrocyte plasma membranes

We have examined the band 3 protein(s) of rabbit erythrocyte membranes by a combination of differential extraction and surface labeling methods. Only one major peptide was labeled when intact red cells were exposed to ¹²⁵I^? and lactoperoxidase; this coincided with band 3. When intact cells were exposed to galactose oxidase followed by [³H]borohydride, numerous surface glycoproteins were labeled, one of which clearly coincided with band 3. Differential extraction with lithium diiodosalicylate revealed one major band 3 glycoprotein which contained both the ¹²⁵I^? and ³H surface labels and three peptides which were unlabeled; these three peptides are apparently not exposed at the cell surface.     

Immunochemical evidence for the transmembrane orientation of glycophorin A. Localization of ferritin-antibody conjugates in intact cells.

Antibodies were raised in rabbits to a 51-amino acid cyanogen bromide-derived peptide of human erythrocyte glycophorin A which has been shown to represent the C-terminal end of the 131-residue polypeptide chain. Antibodies prepared by immunoadsorption were found to be directed against a chymotryptic-derived peptide (residues 102 to 118) of glycophorin A but were unreactive with either intact or proteolytically modified red blood cells. No cross-reactivity was observed with glycophorin B of human or sialoglycoproteins prepared from red blood cells of other mammalian species. Ferritin-antibody conjugates of such sera were applied to thin sections of intact red blood cells (frozen or protein embedded) and were found to localize exclusively to sites distributed uniformly along the inner surfaces of the membrane. No staining was seen on sections prepared from red blood cells from other species nor on sections of human red cells pretreated with unconjugated antisera. These results provide additional evidence in intact, fixed human erythrocytes that glycophorin A has a transmembrane orientation.     

Alkylation of Free Sulfhydryls Fortifies Electroplax Subsynaptic Structures

The cysteine-rich 43,000-dalton peripheral membrane protein, nu 1, is localized at the cytoplasmic face of electroplax and muscle cholinergic synapses, where it is thought to play an important role in the endplate supramolecular structure. The peripheral membrane protein properties of nu 1 are inferred by its removal from nicotinic cholinergic membranes by the action of mild alkali or lithium diiodosalicylate. An interesting property of nu 1 is its high concentration of free sulfhydryl groups, whose exact role in synaptic structure is still largely unknown. Alkylation of free sulfhydryls with N-ethylmaleimide (3 mM) has a profound effect on the association of nu 1 with synaptic membranes, rendering nu 1 unextractable by pH 11 treatment or by lithium diiodosalicylate and, concomitantly, decreasing nu 1's electrophoretic mobility on sodium dodecyl sulfate-polyacrylamide gels. Iodoacetamide and iodoacetate have similar effects, but at concentrations 10- to 100-fold higher than required for N-ethylmaleimide. Furthermore, sulfhydryl modification also stabilizes the association of nicotinic receptor subunits with the detergent-insoluble cytoskeleton. N-Ethylmaleimide treatment increases the fraction of insoluble receptor molecules on extraction with Triton X-100, sodium cholate, or octylglucoside. These results suggest an important role of sulfhydryl groups in the structural stability of the postsynaptic cholinergic membrane.     

Protein organization in Newcastle disease virus as revealed by perturbant treatment.

Treatment of Newcastle disease virus with lithium diiodosalicylate differentially elutes the internally disposed proteins, M and NP, showing that these proteins are extrinsic, i.e., not associated with the lipid hydrophobic core. This selective elution requires disruption of the viral envelope, a process that is maximal at low temperature and influenced by the lipid composition of the virus envelope.     

Incorporation of the transmembrane hydrophobic domain of glycophorin into small unilamellar phospholipid vesicles Ion Flux studies

Human erythrocyte glycophorin is one of the best characterized integral membrane proteins. Reconstitution of the membrane-spanning hydrophobic segment of glycophorin (the tryptic insoluble peptide released when glycophorin is treated with trypsin) with liposomes results in the production of freeze-fracture intrabilayer particles of 80 Å diameter (Segrest, J.P., Gulik-Krzywicki, T. and Sardet, C. (1974) Proc. Natl. Acad. Sci. U.S.A. 71, 3294–3298), with particles appearing at or above a tryptic insoluble peptide concentration of 4 mmol per mol phosphatidylcholine. In the present study, increasing concentrations of tryptic insoluble peptide were added to sonicated small unilamellar egg phosphatidylcholine vesicles and the rate of efflux of ²²Na⁺ was examined by rapid (30 s) gel filtration on Sephadex G-50. Below a concentation of 3–5 mmol tryptic insoluble peptide/mol phosphatidylcholine, ²²Na⁺ efflux occurs at a constant slow rate at given tryptic insoluble peptide concentrations. Above a concentration of 3–5 mM, the rate of efflux is biphasic at given tryptic insoluble peptide concentrations, exhibiting both an initial fast and a subsequent slow component. On the basis of graphic and computer curve-fitting analysis, with increasing tryptic insoluble peptide concentration, the rate of the slow component reaches a plateau at a tryptic insoluble peptide concentration of 3–5 mM and remains essentially constant until much higher concentrations are reached; the fast component increases linearly with increasing tryptic insoluble peptide concentration well beyond 5 mM. The most consistent interpretation of this data is as follows. The slow ²²Na⁺ efflux component is due to perturbations of small unilamellar vesicle integrity by tryptic insoluble peptide monomers. At a tryptic insoluble peptide concentration of 3–5 mmol/mol, a critical concentration is reached following which there is intrabilayer tryptic insoluble peptide self-association. The fast ²²Na⁺ efflux component is due to the increasing presence of tryptic insoluble peptide self-associated multimers the 80-Å particles seen by freeze-fracture electron microscopy) which results in a significantly larger bilayer defect than do tryptic insoluble peptide monomers. The failure of complete saturation of efflux by the fast component is ascribed to the presence of two populations of small unilamellar vesicles, some of which contain tryptic insoluble peptide multimers and some of which do not.Addition of cholesterol to the tryptic insoluble peptide/phosphatidylcholine vesicles decreases the rate of ²²Na⁺ efflux by inhibiting primarily the fast component. Freeze-fracture electron microscopy indicates that the presence of cholesterol has no effect on the size, number or distribution of 80-Å intra-bilayer particles in the tryptic insoluble peptide/phosphatidylcholine vesicles. These results are consistent with a mechanism to explain the fast Na⁺ efflux component involving protein-lipid boundary perturbations.Efflux of ⁴⁵Ca²⁺ from phosphatidylcholine vesicles is also enhanced by incorporation of tryptic insoluble peptide, but only if divalent cations (Ca²⁺ or Mg²⁺) are present in the external bathing media as well as inside the sonicated vesicles. If monovalent Na⁺ only is present in the bathing media no ⁴⁵Ca²⁺ efflux is seen. Under conditions where ⁴⁵Ca²⁺ efflux is seen, both a fast and a slow component are present, although both appear lower than corresponding rate constants for ²²Na⁺ efflux. These results suggest a coordinated mechanism for ion efflux induced by tryptic insoluble peptide and, together with the ²²Na⁺ efflux studies, may have mechanistic implications for the transbilayer phospholipid exchange (flip-flop) suggesed to be induced at glycophorin/phospholipid interfaces (de Kruiff, B., van Zoelen, E.J.J. and van Deenen, L.L.M. (1978) Biochim. Biophys. Acta 509, 537–542).     

Synthetic peptides mimic the assembly of transmembrane glycoproteins

The composition of the intramembranous domains of many receptors are remarkably uniform, yet there is evidence that many transmembrane proteins associate together to form specific noncovalent homo- or heterocomplexes within the membrane. We have synthesized peptides corresponding to transmembrane domains of glycophorin A, glycophorin C, and the interleukin 2-receptor Tac antigen to study the interactions between transmembrane domains in vitro. Synthetic transmembrane glycophorin A peptide formed a complex with native glycophorin and glycoproteins of erythrocyte and K562 cell membranes that was reversible, specific, and could be demonstrated in a natural bilayer system in the absence of detergents. Synthetic glycophorin C and interleukin 2-receptor Tac antigen transmembrane peptides, although similar in amino acid composition, did not interact with glycophorin and did not inhibit the binding of the synthetic glycophorin A transmembrane peptide to native glycophorin. It is proposed that the transmembrane segments of receptor proteins contain not only the structural information necessary for insertion and anchoring but specific binding sites that mediate interactions between transmembrane glycoproteins.