The band 3 protein of the human red cell membrane: a review

The kinetics of intramolecular cross-linking of the band 3 protein in the red blood cell membrane by 4,4'-diisothiocyano dihydrostilbene-2,2'-disulfonic acid (H2DIDS)

The two isothiocyanate groups of the anion transport inhibitor 4,4'-diisothiocyano dihydrostilbene-2-2'-disulfonate (H2DIDS) may react covalently with two lysine residues called a and b that reside on the chymotryptic 60,000 Dalton and 35,000 Dalton segments, respectively, of the band 3 protein of the human erythrocyte membrane. Under suitable conditions, the reaction leads to the establishment of intramolecular cross-links between a and b (M.L. Jennings & H. Passow, 1979, Biochim. Biophys. Acta 554:498-519). In the present work, the time course of the reactions with a and b, and of the establishment of the cross-link were investigated experimentally and compared with simple mathematical models of the reaction sequence. The rates of reaction with a and b were found to increase with increasing pH. Regardless of pH, the rate of reaction with a exceeds that with b several-fold. Once the H2DIDS molecule has reacted with a, the rate of the subsequent reaction of the other isothiocyanate group with b is reduced by about 1/30. The reactions that follow the unilateral attachment to site b are not yet clear. A more detailed analysis of the time course of the cross-linking reaction suggests that a satisfactory description of the kinetics requires the assumption that the H2DIDS binding site may exist in two different states, and that the transition from one state to the other is associated with changes of the reactivities of either lys a alone or of both lys a and b. This led to the formulation of the two-states model of the H2DIDS binding site, which is supported by other pieces of independent evidence. The analysis of the pH dependence of the rate of thiocyanylation of b shows that the apparent pK value of that lysine residue is about 9.9 to 10.0 and hence slightly lower than the intrinsic pK of a lysine residue in an aqueous environment.

Co-operative binding of concanavalin A to a glycoprotein in lipid bilayers

Lectin-binding curves are reported for a concanavalin A receptor glycoprotein in lipid bilayers and intact cells. The results are consistent with previous studies of the structurally dissimilar transmembrane glycoprotein, glycophorin. High-affinity lectin binding to model membranes was influenced by the presence of apparently unrelated macromolecules, which we suggest is an example of receptor modulation by local interactions. Furthermore, high-affinity binding to the model membranes displayed characteristics, including positive cooperativity, similar to those seen with intact cells.

Freeze-fracture cytochemistry: partition of glycophorin in freeze-fractured human erythrocyte membranes

Thin-section and critical-point-dried fracture-labeled preparations are used to determine the distribution and partition of glycophorin-associated wheat germ agglutinin (WGA) binding sites over protoplasmic and exoplasmic faces of freeze-fractured human erythrocyte membranes. Most wheat germ agglutinin binding sites are found over exoplasmic faces. Label is sparse over the protoplasmic faces. These results contrast with previous observations of the partition of band 3 component where biochemical analysis and fracture-label of concanavalin A (Con A) binding sites show preferential partition of this transmembrane protein with the protoplasmic face. Presence of characteristic proportions of WGA and Con A binding sites over each fracture face is interpreted to indicate the operation of a stochastic process during freeze-fracture. This process appears modulated by the relative expression of each transmembrane protein at either surface as well as by their association to components of the erythrocyte membrane skeleton.

Red cell membrane protein anomalies in congenital dyserythropoietic anaemia, type II (HEMP AS)

In all of six cases of congenital dyserythropoietic anaemia, type II (HEMPAS), gel electrophoresis in the presence of SDS revealed abnormally rapid migration of the preponderant integral membrane protein, band 3. After proteolysis of intact cells, the remaining part of the band 3, comprising the intramembrane segment and the cytoplasmic domain, migrated electrophoretically as a single band, identical in mobility to that from normal cells treated in the same manner. The anomaly thus resides in the extracellular domain of the protein, which is the glycosylated part of the chain. Peptide digests of the band 3 showed no evidence of a missing protein segment in the abnormal cells and the amino acid composition of the peptides derived from proteolysis of the extracellular protein of intact cells was also normal. We infer that the anomaly is one of glycosylation. The major glycoproteins, detected by carbohydrate-specific (PAS) stain appear normal in SDS gels. However, when the more sensitive procedure of reacting after electrophoresis with radioiodinated lentil lectin is employed, some additional minor protein components are revealed. In particular one species of apparent subunit molecular weight about 150 000 appeared in all cases of HEMPAS examined and in no normals. This component is not accessible to proteolysis by chymotrypsin or Streptomyces griseus protease, and may be associated with the inner membrane patches, characteristic of the HEMPAS condition. Overall cell shape and microviscosity of the membrane bilayer, as measured by fluorescence polarization of a lipid-soluble fluorophore, were substantially normal in HEMPAS cells.

Discrimination of three parallel pathways of lactate transport in the human erythrocyte membrane by inhibitors and kinetic properties

The transmembrane movements of lactate and other monocarboxylate anions in mammalian erythrocytes have been claimed, by virtue of their sensitivity to SH-reagents, to involve a transfer system different from the classical anion system (Deuticke, B., Rickert, I. and Beyer, E. (1978) Biochim. Biophys. Acta 507, 137-155). Inhibition of monocarboxylate transfer by SH-reagents, however, was incomplete to an extent varying for different monocarboxylates. The transport component insensitive to SH-reagents has now been shown to involve (a) the classical anion-exchange system, as demonstrated by sensitivity to specific disulfonate inhibitors, and (b) nonionic diffusion, as indicated by the characteristic pH- and concentration dependency of this component and its stimulation by aliphatic alcohols. Under physiological conditions about 90% of total lactate movement proceed via the specific system, 5% via the classical anion-transfer system, 5% by nonionic diffusion. These three components of lactate exchange differ in their activation energies. The specific lactate system mediates net fluxes almost as fast as exchange fluxes, in marked contrast to the classical anion-exchange system which mediated halide exchange much faster than halide net movements. The underlying mechanism, for maintenance of electroneutrality, is an OH- -antiport or an H+ -symport as indicated by the particular response of lactate net fluxes to changes of intra- or extracellular pH.

The molecular basis for membrane - cytoskeleton association in human erythrocytes

Spectrin, the major cytoskeletal protein in erythrocytes, is localized on the inner membrane surface in association with membrane-spanning glycoproteins and with intramembrane particles. The presence of a specific, high-affinity protein binding site for spectrin on the cytoplasmic surface of the membrane has been established by measurement of reassociation of spectrin with spectrin-depleted inside-out vesicles. A 72,000 Mr proteolytic fragment of this attachment protein has been purified, which bound to spectrin in solution and competed for reassociation of spectrin with vesicles. A 215,000 Mr polypeptide has been identified as the precursor of the spectrin-binding fragment. The membrane attachment protein for spectrin was named ankyrin, and has been purified and characterized. Ankyrin has been demonstrated to be tightly associated in detergent extracts of vesicles with band 3, a major membrane-spanning polypeptide, and to bind directly to a proteolytic fragment derived from the cytoplasmic domain of band 3. Ankyrin is thus an example of a protein that directly links a cytoplasmic structural protein to an integral membrane protein. The organization of the erythrocyte membrane has implications for more complex cell types since immunoreactive forms of ankyrin distinct from myosin or filamin have been detected by radioimmunoassay in a variety of cells and tissues. Indirect immunofluorescent staining of cultured cells reveals immunoreactive forms of ankyrin in a cytoplasmic meshwork and in a punctate distribution over nuclei. The staining changes dramatically during mitosis, with concentration of stain at the spindle poles in metaphase and intense staining of the cleavage furrow during cytokinesis.

31P nuclear magnetic resonance studies of the phospholipid-protein interface in cell membranes

Both native and recombined membrane systems from the human erythrocyte membrane and the rabbit sarcoplasmic reticulum have been studied with 31P Nuclear Magnetic Resonance (NMR). We compare intensities of the anisotropic 31P resonance exhibited by these membranes with the intensity expected from the known phospholipid content of the membranous sample. In a recombinant with human erythrocyte glycophorin, a component of the phospholipid is "missing" from the 31P NMR resonance, apparently due to a severe broadening of the resonance of that component. Approximately 29 phospholipid molecules were found immobilized per glycophorin molecule in the membrane, regardless of the phospholipid:protein ratio. Cholesterol may inhibit the immobilization of phospholipids by glycophorin. Recombinants with band three from the human erythrocyte membrane contain an immobilized phospholipid component, analogous to the results with glycophorin. 31P NMR data from the native sarcoplasmic reticulum membrane also revealed an immobilized phospholipid component whose magnitude is independent of temperature between 30 degrees C and 45 degrees C. Extensive papain proteolysis of the membrane completely digests the Ca++ Mg++ ATPase and removes the immobilization of phospholipids noted in the intact membrane. Limited trypsin cleavage, however, does not completely remove the immobilized component; salt reduces the immobilized component.

The IgG binding function of the normal red cell plasma membrane: identification of integral polypeptides that bind IgG

Non-immune IgG binds to red cell integral membrane proteins obtained by mild alkaline extraction of ghosts. Detergent gel chromatography and electrophoretic analyses of IgG-membrane protein complexes obtained by nonionic detergent solubilization and affinity binding to protein A indicate that three polypeptides participate in the binding of IgG. These have apparent molecular weights of 90 000, 44 000 and 22 000 and are present in a 1:3:0.9 stoichiometry. Evidence obtained indicates that the major sialoglycoproteins are not involved in this type of binding.

Degradation of band-3 glycoprotein in vitro by a protease isolated from human erythrocyte membrane

The use of soybean-trypsin-inhibitor-Sepharose-4B to purify a protease present in human erythrocyte membranes is described. The fraction bound in the presence of calcium to the affinity absorbent is active on band-3 glycoprotein in a non-ionic detergent solution at neutral pH. Band-3 glycoprotein is degraded into components having the mobilities of the proteins of bands 4.5, 7 and of lower molecular weights. When calcium is omitted from the membrane extract, an inactive form of this enzyme can be purified. By DEAE-cellulose chromatography this inactive form can be converted into the active form, presumably by dissociation of an enzyme-inhibitor complex.

Modification by papain of the structure and function of band 3, the erythrocyte anion transport protein

Extracellular papain is known to inhibit the anion transport function of the band 3 protein of the human red blood cell membrane. Previous work [Jennings, M. L., & Passow, H. (1979) Biochim. Biophys. Acta 554, 498-519] had suggested that this inhibition may result from the removal by papain of 5 000-10 000 daltons from the 35 000-dalton chymotryptic peptide of band 3. The present work shows, however, that papain also removes a small peptide from the C terminus of the 60 000-dalton chymotryptic peptide. The C-terminal amino acid sequence of this peptide is -Lys-Thr-Tyr. Whether or not this newly discovered action of papain is responsible for inhibiting anion transport is unknown. The effects of extracellular papain on the band 3 function have been characterized in detail. Papain inhibits Cl-Cl exchange in a high Cl medium by almost 90%. This inhibition appears to result from inhibition of the efflux step in the catalytic cycle for the transport, because papain does not inhibit the anion transport when it is assayed under influx-limited conditions. Moreover, since papain has no detectable effect on the dissociation constant for extracellular substrate (SO4) binding, the material removed by papain cannot be involved closely in the outward-facing substrate site. In contrast, removal of this material strongly (12-fold) reduces the affinity of the inhibitor 4,4'-dinitro-2,2'-stilbenedisulfonate for outward-facing sites. Therefore, stilbenedisulfonate binding involves portions of the band 3 molecule which are not intimately related to substrate binding.

Erythrocyte membrane protein band 3: its biosynthesis and incorporation into membranes

Band 3, a transmembrane protein that provides the anion channel of the erythrocyte plasma membrane, crosses the membrane more than once and has a large amino terminal segment exposes on the cytoplasmic side of the membrane. The biosynthesis of band 3 and the process of its incorporation into membranes were studied in vivo in erythroid spleen cells of anemic mice and in vitro in protein synthesizing cell-free systems programmed with polysomes and messenger RNA (mRNA). In intact cells newly synthesized band 3 is rapidly incorporated into intracellular membranes where it is glycosylated and it is subsequently transferred to the plasma membrane where it becomes sensitive to digestion by exogenous chymotrypsin. The appearance of band 3 in the cell surface is not contingent upon its glycosylation because it proceeds efficiently in cells treated with tunicamycin. The site of synthesis of band 3 in bound polysomes was established directly by in vitro translation experiments with purified polysomes or with mRNA extracted from them. The band-3 polypeptide synthesized in an mRNA-dependent system had the same electrophoretic mobility as that synthesized in cells treated with tunicamycin. When microsomal membranes were present during translation, the in vitro synthesized band-3 polypeptide was cotranslationally glycosylated and inserted into the membranes. This was inferred from the facts that when synthesis was carried out in the presence of membranes the product had a lower electrophoretic mobility and showed partial resistance to protease digestion. Our observations indicate that the primary translation product of band-3 mRNA is not proteolytically processed either co- or posttranslationally. It is, therefore, proposed that the incorporation of band 3 into the endoplasmic reticulum (ER) membrane is initiated by a permanent insertion signal. To account for the cytoplasmic exposure of the amino terminus of the polypeptide we suggest that this signal is located within the interior of the polypeptide. a mechanism that explains the final transmembrane disposition of band 3 in the plasma membrane as resulting from the mode of its incorporation into the ER is presented.

Phosphate transport in human red blood cells: concentration dependence and pH dependence of the unidirectional phosphate flux at equilibrium conditions

The concentration dependence and the pH dependence of the phosphate transport across the red cell membrane were investigated. The unidirectional phosphate fluxes were determined by measuring the 32P-phosphate self-exchange in amphotericin B (5 mumol/liter) treated erythrocytes at 25 degrees C. The flux/concentration curves display an S-shaped increase at low phosphate concentrations, a concentration optimum in the range of 150 to 200 mM phosphate and a self-inhibition at high phosphate concentrations. The apparent half-saturation concentrations, P(0.5), range from 50 to 70 mM and are little affected by pH. The self-inhibition constants, as far as they can be estimated, range from 400 to 600 mM. The observed maximal phosphate fluxes exhibit a strong pH dependence. At pH 7.2, the actual maximal flux is 2.1 X 10(-6) moles . min-1 . g cells-1. The ascending branches of the flux/concentration curves were fitted to the Hill equation. The apparent Hill coefficients were always in the range of 1.5-2.0. The descending branches of the flux/concentration curves appear to follow the same pattern of concentration response. The flux/pH curves were bell-shaped and symmetric with regard to their pH dependence. The pH optimum is at approximately pH 6.5-6.7. The apparent pK of the activator site is in the range of 7.0 to 7.2, while the apparent pK for the inactivating site is in the range of 6.2 to 6.5. The pK-values were not appreciably affected by the phosphate concentration. According to our studies, the transport system possesses two transport sites and probably two modifier sites as indicated by the apparent Hill coefficients. In addition, the transport system has two proton binding sites, one with a higher pK that activates and one with a lower pK that inactivates the transport system. Since our experiments were executed under self-exchange conditions, they do not provide any information concerning the location of these sites at the membrane surfaces.

Protein involvement in structural transition of erythrocyte ghosts. Use of thermal gel analysis to detect protein aggregation

In this study, it is shown that systematic temperature-induced protein aggregation occurs on the erythrocyte membrane by intermolecular disulfide bond formation. Specific protein bands disappear from acrylamide gel profiles over rather narrow temperature regions. The aggregation appears to be the result of irreversible structural transitions of the membrane, which can be seen in a sensitive scanning calorimeter. When this method of thermal gel analysis is used, the results suggest that spectrin is a participant in the A transition, that bands 2.1, 4.1, and 4.2 and the cytoplasma portion of 3 are involved in the B transition, and that the transmembrane portion of band 3 may undergo changes in the C transition, previously shown to occur in the anion transport domain of the membrane. The aggregation of specific proteins in the narrow temperature region of these transitions persists as the transitions are moved around on the temperature axis by varying solution conditions. The assignment of particular proteins to specific transitions is reinforced by selective extraction of membrane proteins. Large variations in both the calorimetry and the aggregation pattern occur as salt concentration is increased from 77 mosm to 310 mosm, which is manifested in the splitting of the B transition into two separate transitions, B1 and B2. It is speculated that this occurs as the result of a structural change which may involve components of the cytoskeletal network.

Freeze-fracture cytochemistry: replicas of critical point-dried cells and tissues after fracture-label

Applications of the new fracture-labeling techniques for the observation of cytochemical labels on platinum-carbon replicas are described. Frozen cells, embedded in a cross-linked protein matrix, and frozen tissues are fractured with a scalpel under liquid nitrogen, thawed, labeled, dehydrated by the critical point drying method, and replicated. This method allows direct, high-resolution, two-dimensional chemical and immunological characterization of the cellular membranes in situ, as well as detection of sites within cross-fractured cytoplasm and extracellular matrix.

Some properties of alkali-extracted red cell ghost membranes

The properties of integral membrane proteins obtained by dilute alkali extraction of red cell ghosts were examined. A variety of conditions promoted the disulfide-mediated aggregation of integral membrane proteins, principally band 3. Procedural modifications which minimized aggregation were the use of EDTA and S-alkylation. Integral membrane proteins were solubilized under non-denaturing conditions using Brij 36T, a lauryl polyoxyethylene ether with an NMR-determined average chain length of 8.2 (oxyethylene) units. Detergent gel filtration revealed a chromatographic shoulder due to aggregated band 3 when membrane proteins were not alkylated. Analyses of the column profile also revealed a discrete peak for sialoglycoproteins and two phosphate peaks, an early one due to phospholipid and a later one not identified, but probably due to phosphoinositide.

Mediated transport of anions in band 3-phospholipid vesicles

Band 3 protein, extracted from human erythrocyte membranes by Triton X-100, was recombined with egg lecithin/cholesterol mixtures to form small unilamellar vesicles at a yield of 15-20%. These systems exhibited sulfate fluxes which were inhibitable by stilbene disulfonates and other inhibitors. Maximal inhibition could only be obtained when inhibitors were present at both membrane surfaces. Inhibitor constants I50 were higher than in the native membrane. Quantitatively, transport function was retained at least 60%, as related to the amount of protein involved. Sulfate transport in the recombinates resembled transport in the native membrane with respect to temperature dependence (Ea = 29-32 kcal/mol), pH dependence between pH 6.5 and 7.8, and the relationship between new and exchanges fluxes. In contrast to the native cell, concentration dependence was linear up to 80 mM sulfate, which may be indicative of a lowered affinity for the substrate. Lactate transport in these systems, although substantial, was insensitive to stilbene disulfonates as well as to mercurials, indicating that band 3 is not involved in the specific monocarboxylate transfer in the erythrocyte. Anion transport in band 3-lipid recombinates was insensitive to cholesterol between 0 and 27 mol%. Treatment with proteases, while not affecting transport per se, abolished sensitivity to stilbene disulfonate inhibitors. These observations indicate a number of disturbances of band 3 after recombination, in spite of a preservation of the major transport properties.

The anion-transfer system of erythrocyte membranes. N-(7-Nitrobenzofurazan-4-yl)taurine, a fluorescent substrate-analogue of the system

The fluorescent probe Nbd-Tau [N-(7-nitrobenzofurazan-4-yl)taurine] was synthesized and evaluated as a potential substrate of the anion-transport system of human erythrocyte membrane. The probe inhibited Cl- exchange in a competitive manner from either surface of the membrane, displaying Ki values in the mM range at the inner surface and in the microM range at the outer surface. Inhibition from within cells was via interaction with Cl--transport sites, whereas from it was via interaction with sites of unidentified nature. Nbd-Tau efflux from cells was monitored fluorimetrically in a continuous mode by a novel method that circumvents separation of the cells from the medium. Using this method, it is shown that Nbd-Tau efflux fulfils the following criteria of a substrate of the anion transport system: (a) susceptibility to classical and specific inhibitors of the system; (b) competitive inhibition with Cl- for anion-transport sites; and (c) temperature coefficient comparable with that of Cl- exchange. The fluorometric method is highly sensitive, versatile, and kinetically informative. With minor modifications it can be used for measuring anion transport across "ghost" and isolated membrane vesicles.

Anti-Rho(D) IgG binds to band 3 glycoprotein of the human erythrocyte membrane

Alkali-extracted erythrocyte ghost membranes from Rho(D)-positive and Rho(D)-negative donors were incubated with human immune anti-Rho(D) IgG and nonimmune IgG. After sensitization with IgG, the integral membrane proteins were solubilized in Brij 36T nonionic detergent and chromatographed by gel filtration. There was a distinct resolution of IgG into free and membrane-complexed forms. The IgG-complexed membrane proteins were isolated by the use of a staphylococcal protein A affinity support. The protein A-bound complexes were examined for polypeptide composition by gel electrophoresis after elution. Only Rho(D)-positive membrane proteins incubated with immune anti-Rho(D) IgG revealed intact band 3. Control Rh-negative membrane proteins that had reacted with immune anti-Rho(D) IgG and the Rh-positive membranes that had reacted with nonimmune IgG showed only low molecular weight fragments of band 3 that bound nonspecifically to IgG. Arguments are presented supporting a band 3 localization for the Rh antigen.

A relationship between anion transport and a structural transition of the human erythrocyte membrane

Scanning microcalorimetry was employed as an aid in examining some structural features of the anion transport system in red blood cell vesicles. Two structural transitions were previously shown to be sensitive to several covalent and non-covalent inhibitors of anion transport in red cells. In this study, these transitions were selectively removed, either thermally or enzymatically, and the subsequent effect on 35SO2- 4 efflux in red cell vesicles was determined. It is shown that removal of one of these transitions (B2) has a negligible inhibitory effect on anion transport. Cytoplasmic, intermolecular disulfide linkages between band 3 dimers are known to form during the B2 transition. The integrity of the 4,4-diisothiocyanostilbene-2,2-disulfonate-sensitive C transition, on the other hand, is shown to be a requirement for anion transport. The localized region of the membrane giving rise to this transition contains the transmembrane segment of band 3, as well as membrane phospholipids. The calorimetric results suggest a structure of band 3 which involves independent structural domains, and are consistent with the transmembrane segment playing a direct role in the transport process.

Fracture-label:O cytochemistry of freeze-fracture faces in the erythrocyte membrane

A method--"fracture label"--is described for the cytochemical labeling of the membrane faces produced by freeze-fracture. Human erythrocytes embedded in a crosslinked matrix are frozen, fractured in liquid nitrogen, thawed, labeled, and cut into thin sections. Electron microscope observation of the fracture faces shows preferential partition of concanavalin A binding sites with the inner half of the membrane. This signifies that, during freeze-fracture, binding sites are dragged from the outer surface across the outer ("exoplasmic") half of the membrane and retained on the protoplasmic fracture face (face P). The fracture process results in exposure of new anionic sites on face P. Fracture-label can be applied to the cytochemical characterization of the cellular components exposed by freeze-fracture of isolated cells and tissues.