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

Rotational diffusion of band 3 in erythrocyte membranes. 1. Comparison of ghosts and intact cells

The rotational diffusion of eosin-labeled 3 in human erythrocyte cells and hemoglobin-free ghosts at 37 degrees C has been studied in detail by polarized delayed luminescence. The time-resolved anisotropy with both cells and freshly prepared ghosts is similar, decaying with well-resolved rotational correlation times of 0.03, 0.2, and greater than or equal to 1 ms. Mild proteolytic removal of the water-soluble 41-kDa cytoplasmic domain of band 3 in ghosts results in a drastic increase in the fractional contributions of the two fastest depolarizing components. Our results, taken together with other data in the literature, imply that several classes of band 3 that differ greatly in mobility exist in ghosts and intact cells. The mobility of one class is hindered due to complexation with other membrane or cytoplasmic proteins mediated via the 41-kDa cytoplasmic domain. However, another class of band 3 molecules exists as homo-or heterooligomeric complexes larger than a dimer that are stabilized by hydrophobic interactions involving the intramembranal domain. Finally, the presence of the (previously undetected) 0.03-ms anisotropy component strongly suggests that a significant fraction of band 3 in both ghosts and intact cells is highly mobile and diffuses at the rate expected for a freely rotating dimer in the erythrocyte membrane.

Brain membrane protein band 3 performs the same functions as erythrocyte band 3

We report the presence of band 3 protein(s) in mammalian brain that performs the same functions as those of erythroid band 3. These functions are anion transport, ankyrin binding, and generation of senescent cell antigen, an aging antigen that terminates the life of cells. Structural similarity of brain and erythroid band 3 is suggested by the reaction of antibodies to synthetic peptides of erythroid band 3 with brain band 3, the inhibition of anion transport by the same inhibitors, and an equal degree of inhibition of brain and erythrocyte anion transport by synthetic peptides of erythroid band 3 (pep-ANION 2, residues 588-602; pep-COOH, residues 812-827; pep-COOH-N6, residues 813-818). One of these segments, pep-COOH, contains antigenic determinants of senescent cell antigen. These findings suggest that the transport domains of erythroid and neural band 3 are similar functionally and structurally and support the hypothesis that the immunological mechanism of maintaining homeostasis is a general physiologic process for removing senescent and damaged cells in mammals and other vertebrates.

Surfaces of cryosections: is cryosectioning 'cutting' or 'fracturing'?

In order to determine if cryosectioning involves 'fracturing' or 'cutting' we examined the surfaces obtained in cryosectioning by a metal-replicating procedure commonly used in freeze-fracture microscopy. Platinum-carbon replicas were made of the surfaces of both the sections and the complementary surfaces of the sample stubs from which the sections were cut. When samples of frozen red cells were sectioned at -120 degrees C with large knife advancements (1 micron), the chips produced did not resemble sections. Membrane fracture faces, produced by splitting of the lipid bilayer, were found in electron micrographs of replicas of the sample stubs. This demonstrates that a cryomicrotome can be used to produce large intact replicas. When dull knives were used with small knife advancements, both smooth and fractured regions were found. The sections produced with dull knives had a snowflake appearance in the light microscope. When sharp knives were used with small advancements (0.1 microns), replicas of the surfaces were free of fracture faces and the sections had a cellophane-like appearance in the light microscope. Therefore, in cryosectioning a different process other than 'fracturing' is responsible. This 'cutting' process may be micromelting of a superficial layer by the mechanism of melting-point depression from the pressure exerted by the sharp edge of the knife.

Molecular biology of the anion exchanger gene family

The gene family of anion exchangers consists of at least four or five members, of which three have been characterized at the cDNA level. AE1-3 encode polypeptides that share significant homology with the erythrocyte anion exchanger, band 3 (AE1). Expression of cDNAs encoding these genes in heterologous systems confirms that this sequence similarity is reflected in the capacity to mediate reversible Cl/HCO3 exchange. While the NH2-terminal domain of band 3 is known to interact with several cytoplasmic proteins in erythrocytes, the function of the analogous domains of AE2 and AE3 remains unknown. The AE1 gene is expressed coordinately with other erythroid genes during erythropoiesis in both avian and mammalian erythroid progenitor cells. In addition, AE1 is expressed at the basolateral plasma membrane of the acid-secreting intercalated cells of the kidney. AE2 is expressed in a number of epithelial and nonepithelial cells; it may be expressed in the Golgi apparatus of some of these cells. AE3 is expressed in excitable tissues, including neurons and muscle. It is likely that these proteins play a role in regulation of intracellular pH and chloride in their respective tissue. Understanding of the physiological roles of these proteins, both for ion transport and for plasma membrane organization, remains a central issue.

Antigenic determinants of the cytoplasmic domain of band 3 from bovine erythrocyte membrane

Rabbit antibodies were prepared against the cytoplasmic 38K-Da fragment of bovine band 3 and the immunological cross-reactivity with human, murine, rat, and chicken band 3 was examined. The antibodies cross-reacted with human and rodent band 3, indicating that there is an antigenic determinant(s) common to primate and nonprimate species. However, the antibodies did not recognize chicken band 3. Antigenic sites on the 38K-Da fragment were determined via amino acid sequence and immunoblotting analyses of proteolytic peptides of the fragment. Positions of antigenic determinants which were assumed to be common to primate and nonprimate species were mapped to the areas of residues 127-160 and of residues 259-304 in the primary structure of human band 3. Another epitope(s), which is absent in human band 3, existed in a region having a bovine-specific amino acid sequence. In addition, comparison of sequence data from different species showed that a proposed hinge region and a tryptophan-rich region on the cytoplasmic domain of band 3 [P. S. Low et al. (1984) J. Biol. Chem. 259, 13,070-13,076; R. R. Kopito and H. F. Lodish (1985) Nature (London) 316, 234-238] are also conserved in the bovine case.

Degradation of skeletal muscle plasma membrane proteins by calpain

Observations described here provide the first demonstration that calpain (Ca2+-dependent cysteine protease) can degrade proteins of skeletal muscle plasma membranes. Frog muscle plasma membrane vesicles were incubated with calpain preparations and alterations of protein composition were revealed by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Calpain II (activated by millimolar concentrations of Ca2+) was isolated from frog skeletal muscle, but the activity of calpain I (activated by micromolar concentrations of Ca2+) was lost during attempts at fractionation. Calpain I obtained from skeletal muscle and erythrocytes of rats was tested instead, and exerted effects similar to those of frog muscle calpain on the membrane proteins. All of the calpain preparations caused striking losses of a major membrane protein of molecular mass of approximately 97 kDa, designated band c, and diminution of a thinner band of approximately 200 kDa. There were concomitant increases in 83- and 77-kDa polypeptides. These effects were absolutely dependent on the presence of free Ca2+, and were completely blocked by calpastatin, a specific inhibitor of calpain action. Frog muscle calpain differed only in being relatively more active at 0 degree C than were the calpains from rat tissues. Experimental observations suggest that calpain acts at the cytoplasmic surface of the plasma membrane.

Cytoskeletal restraints of band 3 rotational mobility in human erythrocyte membranes

The interaction of band 3 with cytoskeletal proteins was investigated in erythrocyte membranes by measuring the rotational mobility of band 3 using the method of transient dichroism. It was found that selective proteolysis of ankyrin, a protein known to link band 3 to the spectrin-actin network, had no significant effect on band 3 rotation. Incubating ghosts to 70 degrees C, at which temperature ankyrin is expected to be denatured, also had no effect. It thus appears probable that linkage of band 3 to the cytoskeleton via ankyrin does not act as a restraint on band 3 rotational motion. It is suggested that this is a consequence of flexibility in the cytoskeletal structure. In further investigations of the effect of heat treatment, a large enhancement of band 3 rotational mobility was found to result from incubation of intact cells for 1 h at 50 degrees C. This effect was not observed if ghosts were subjected to the same treatment, nor did it occur if the incubation of cells was performed at 47 degrees C. These findings, in combination with previous studies of band 3 rotational mobility, indicate that the interactions which restrain band 3 are likely to be more complex than commonly envisaged.

Genomic organization of the glyceraldehyde-3-phosphate dehydrogenase gene family of Caenorhabditis elegans

Glyceraldehyde-3-phosphate dehydrogenase (GAPDHase) is encoded by four genes designated gpd-1 through gpd-4 in the nematode Caenorhabditis elegans. gpd-1 has been isolated and sequenced, and is shown here to have a nearly identical copy (gpd-4) with respect to coding and regulatory flanking sequence information as well as to the placement of its two introns. Both genes, which are separated by 250,000 to 300,000 base-pairs were assigned to chromosome II by in situ hybridization and physically linked to a DNA polymorphism located near unc-4 on the genetic map. The genes gpd-2 and gpd-3 are also nearly identical with each other but differ from the gpd-1 and gpd-4 pair with respect to the positions of their two introns and a cluster of amino acid changes within the amino-terminal region of the enzyme. Furthermore, one gene from each pair (gpd-4 and gpd-2) exhibits a single amino acid substitution at positions heretofore known to be conserved in all other systems so far examined including the extreme thermophiles. gpd-2 and gpd-3 are organized as a direct tandem repeat separated by only 244 base-pairs. They have been assigned to an 85,200 base-pair contig that maps to the left end of the X chromosome. The absence of gpd-3 from C. elegans var. Bergerac was used as a marker to map the gpd-2,3 gene pair near unc-20. Northern analyses have shown that gpd-1 and gpd-4 are preferentially expressed in embryos, while the expression of gpd-2 and gpd-3 increases during postembryonic development. These analyses indicate that the gpd-1,4 gene pair encodes the minor isoenzyme, GAPDHase-1, present in all cells of the nematode while the other gene pair (gpd-2,3) encodes the major isoenzyme, GAPDHase-2, preferentially expressed in the bodywall muscle. The G + T-rich and T-rich regions essential for vertebrate beta-globin polyadenylation were also observed for gpd-3.

Sequence of the Lyb-2 B-cell differentiation antigen defines a gene superfamily of receptors with inverted membrane orientation

Lyb-2 is a mouse B-cell differentiation antigen expressed on the surface of pre-B cells and B cells but not on terminally differentiated antibody-secreting plasma cells. Lyb-2 has been shown to play a role in B-cell activation and differentiation and may be a receptor for a B-cell growth factor or lymphokine. We have isolated and sequenced cDNA encoding the Lyb-2.1 allele. Lyb-2 mRNA is expressed only in B-lineage cells and is absent from antibody-secreting cell lines. The predicted protein contains 354 amino acids and is lacking an amino-terminal signal peptide. The protein is shown to be oriented with its carboxyl terminus external to the cell. Sequence comparisons demonstrate that Lyb-2 is homologous to the asialoglycoprotein receptor and to CD23, the B-cell-specific Fc receptor for IgE, both of which are oriented with their carboxyl termini external to the cell. These molecules, therefore, constitute a gene superfamily of cell surface receptors with inverted membrane orientation.

Structure and deformation properties of red blood cells: concepts and quantitative methods

The lamellar configuration of the red cell membrane includes a (liquid) superficial bilayer of amphiphilic molecules supported by a (rigid) subsurface protein meshwork. Because of this composite structure, the red cell membrane exhibits very large resistance to changes in surface density or area with very low resistance to in-plane extension and bending deformations. The primary extrinsic factor in cell deformability is the surface area-to-volume ratio which establishes the minimum-caliber vessel into which a cell can deform (without rupture). Within the restriction provided by surface area and volume, the intrinsic properties of the membrane and cytoplasm determine the deformability characteristics of the red cell. Since the cytoplasm is liquid, the static rigidity of the cell is determined by membrane elastic constants. These include an elastic modulus for area compressibility in the range of 300-600 dyn/cm, an elastic modulus for in-plane extension or shear (at constant area) of 5-7 X 10(-3) dyn/cm, and a curvature or bending elastic modulus on the order of 10(-12) dyn.cm. Even though small, the surface rigidity of the cell membrane is sufficient to return the membrane capsule to a discoid shape after deformation by external forces. Viscous dissipation in the peripheral protein structure (cytoskeleton) dominates the dynamic response of the cell to extensional forces. Based on a time constant for recovery after extensional deformation on the order of 0.1 sec, the coefficient of surface viscosity is on the order of 10(-3) dyn.sec/cm. On the other hand, the dynamic resistance to folding of the cell appears to be limited by viscous dissipation in the cytoplasmic and external fluid phases. Dynamic rigidities for both extensional and folding deformations are important factors in the distribution of flow in the small microvessels. Although the red cell membrane normally behaves as a resilient viscoelastic shell, which recovers its conformation after deformation, structural relaxation and failure lead to break-up and fragmentation of the red cell. The levels of membrane extensional force which is two orders of magnitude less than the level of tension necessary to lyse vesicles by rapid area dilation. Each of the material properties ascribed to the red cell membrane plays an important role in the deformability and survivability of the red cell in the circulation over its several-month life span.

Effect of stilbenedisulfonate binding on the state of association of the membrane-spanning domain of band 3 from bovine erythrocyte membrane

The membrane-spanning domain of bovine band 3, the anion transport protein of erythrocyte membrane, was purified in the presence of nonaethyleneglycol lauryl ether (C12E9) and the effect of a covalent attachment of 4,4'-diisothiocyanostilbene-2,2'-disulfonate (DIDS), a potent transport inhibitor, on the state of association of the domain isolated (the 58 kDa fragment) was studied via gel filtration, gel electrophoresis and sedimentation velocity experiments. It was indicated that the DIDS-unlabeled fragment in C12E9 solution forms heterogeneous aggregates which are larger in size than the dimer. This contrasted with the behavior that bovine band 3 is present as dimers or tetramers in the same medium (Nakashima and Makino (1980) J. Biochem. 88, 933-947). When DIDS was covalently attached, the fragment was present as a single molecular species which was indicated to be a dimer by molecular weight determination. The secondary structure of the fragment was not affected by DIDS. The change in the state of association caused by the DIDS-binding was also found in the presence of sucrose monolaurate (SE12), which was a more potent detergent for extraction of the 58 kDa fragment from membranes than C12E9. However, the complex with SE12 was extremely unstable.

Degradation of the human erythrocyte membrane band 3 studied with monoclonal antibody directed against an epitope on the cytoplasmic fragment of band 3

The mouse hybridoma monoclonal antibody BIII.136 of the IgG2a class is specific for human erythrocyte band-3 protein. It was shown by means of immunoblotting and immunoprecipitation assays that the antibody recognized an epitope located in the cytoplasmic pole of the band-3 molecule within approximately 20 kDa from the N-terminal end. The N-terminal fragments of band-3 protein, migrating in SDS/polyacrylamide gel electrophoresis in the 60-kDa, 40-kDa and 20-kDa regions, were detected with the antibody in untreated red-cell membranes as products of autolysis of band-3 protein. A correlation was found between the amount of these fragments and erythrocyte age, which suggests that partial degradation of band 3 proceeds in vivo during senescence of erythrocytes. The further degradation of band-3 protein in vitro was not observed in intact erythrocytes stored at 4 degrees C, but progressed distinctly after hemolysis of red cells, during washing and storing the membranes.

Sialic acid concentration in erythrocyte membrane subfractions in patients with myotonic dystrophy and healthy controls

Previous studies have shown a selective reduction of the sialic acid concentration in erythrocyte membranes in patients with myotonic dystrophy. In order to locate this deficiency, chloroform/methanol/H2O extractions of erythrocyte membranes were analyzed in patients with myotonic dystrophy and in matched healthy reference individuals. In the patients, significant reductions of the sialic acid concentration were found in the aqueous phase (p = 0.03) containing mainly glycophorin A as well as in the band-3-containing interphase (p less than 0.005). These findings may be related to certain previously reported membrane abnormalities in myotonic dystrophy.

Functional topography of band 3: specific structural alteration linked to functional aberrations in human erythrocytes

Band 3 is the major anion transport polypeptide of erythrocytes. It appears to be the binding site of several glycolytic enzymes. Structurally, band 3 is the major protein spanning the erythrocyte membrane and connects the plasma membrane to band 2.1, which binds to the cytoskeleton. In the present study, we report an alteration of band 3 molecule that is associated with the following changes: erythrocyte shape change from discoid to "thorny cells" (acanthocytes), restriction of rotational diffusion of band 3 in the membrane, increase in anion transport, and decrease in the number of high-affinity ankyrin-binding sites. Changes in erythrocyte IgG binding, glyceraldehyde-3-phosphate dehydrogenase, fluorescence polarization (indicative of membrane fluidity), and other membrane proteins as determined by polyacrylamide gel electrophoresis were not detected. Cells containing the altered band 3 polypeptide were obtained from individuals with abnormal erythrocyte morphology. Two-dimensional peptide maps revealed differences in the Mr 17,000 anion transport segment of band 3 consistent with additions of tyrosines or tyrosine-containing peptides. The data suggest that (i) this alteration of band 3 does not result in accelerated aging as does cleavage and (ii) structural changes in the anion transport region result in alterations in anion transport.

Dynamic association of band 3 with triton shells in human erythrocyte ghosts

To test a possibility that free band 3 and ankyrin-linked band 3 are exchanged in situ, band 3 was labeled with 125I, using intact red blood cells and lactoperoxidase. The cytoplasmic surface of this labeled band 3 was considered to be intact. When Triton shells were incubated with Triton supernatants prepared from 125I-labeled intact erythrocytes at 37 degrees C in the presence of Mg-ATP under isotonic conditions, the incorporation of free 125I-labeled band 3 to shells was observed. This incorporation was affected by the presence of Triton X-100 in the incubation mixture, and significantly decreased when the content of Triton X-100 was less than 0.04% (v/v). On the other hand, ankyrin-linked 125I-labeled band 3 was released when shells prepared from 125I-labeled intact erythrocytes were incubated with the Triton supernatants at 37 degrees C under the same condition as when free 125I-labeled band 3 incorporation was observed. These results strongly suggest that free and ankyrin-linked band 3 exchanged with each other in the presence of Triton X-100. A water-soluble 43 kDa fragment of band 3 inhibited the incorporation of free 125I-labeled band 3 to the shells and also inhibited the Mg-ATP-dependent shape change of ghosts in the absence of Triton X-100. Both of these inhibitory effects remained, even after 10 min of heat treatment at 100 degrees C, but drastically decreased by treatment with trypsin. Our results strongly suggest that a dynamic exchange of the free band 3 for ankyrin-linked band 3 may occur in intact erythrocytes, and it may even contribute to the shape change of erythrocytes.

Interaction of glyceraldehyde-3-phosphate dehydrogenase with the cytoplasmic pole of band 3 from bovine erythrocyte membrane: the mode of association and identification of the binding site of band 3 polypeptide

Four fragments derived from the cytoplasmic pole of bovine band 3 were isolated, and their ability to bind glyceraldehyde-3-phosphate dehydrogenase from bovine erythrocyte and their amino-terminal primary structure were examined. It was suggested that the 50-kDa fragment, an entire cytoplasmic pole of band 3, contained the blocked amino-terminal end of band 3. Three other fragments, 45-, 39-, and 38-kDa fragments, were produced by cleavage at distances of molecular weight 5000, 11,000, and 12,000 respectively, from the amino-terminus of the 50-kDa fragment. Among these, the 50- and 45-kDa fragments complexed with the enzyme to inhibit its catalytic activity under conditions of low ionic strength, in a fashion similar to that in humans. Affinity for the enzyme was not significantly affected by disruption of the higher order structure of the fragments. The enzyme was found to be inactivated by association with synthetic polyanions, accompanied by conformational alteration. This supports participation of electrostatic interactions as the holding force between the enzyme and band 3, as suggested by I-H. Tsai et al. [1982) J. Biol. Chem. 257, 1438-1442). The 45-kDa fragment was just as potent an inhibitor of the enzyme as the parent fragment, and its amino-terminal region displayed a polyanionic character. These results allow us to map the enzyme binding site of bovine band 3 to a distance of molecular weight approximately 5000 from the amino-terminal end of band 3. Furthermore, comparison of sequence data from different species showed that the species-specific region of band 3 polypeptide centers around the amino-terminal portion.

The glyceraldehyde-3-phosphate dehydrogenase gene family in the nematode, Caenorhabditis elegans: isolation and characterization of one of the genes

The isolation and genomic sequence of one of possibly four glyceraldehyde-3-phosphate dehydrogenase genes in the nematode, Caenorhabditis elegans is presented. The complete nucleotide sequence of the coding as well as the noncoding flanking regions of this gene has been determined. The deduced amino-acid sequence agrees with the sequence of typical glyceraldehyde-3-phosphate dehydrogenase enzymes and its molecular weight of 36,235 agrees with its size determined previously (Yarbrough, P. and Hecht, R. (1984) J. Biol. Chem. 259, 14711-14720). That this isolated gene encodes a nematode glyceraldehyde-3-phosphate dehydrogenase is additionally confirmed by demonstrating its immunoreactivity to an anti-nematode glyceraldehyde-3-phosphate dehydrogenase antibody after its expression as a fusion protein with dihydrofolate reductase. Codon utilization follows a pattern typical of other expressed nematode genes. The gene is split by two introns that are highly conserved in comparison to other introns observed in C. elegans. The placement of one of these introns is conserved with respect to the chicken glyceraldehyde-3-phosphate dehydrogenase gene. Within the 5' flanking sequence homology to actin and the homology 2 block of the major myosin gene (unc-54) is noted. It is of interest that the 3' flanking region contains a CAAAT box, followed by a TATAAT box, before an open reading frame of a closely linked gene that also contains a small AT-rich intron with the nematode consensus splice junction.

Determination of polypeptide chain molecular weights of human and bovine band 3 protein from erythrocyte membranes by low-angle laser light scattering combined with high-performance gel chromatography in the presence of sodium dodecyl sulfate

Polypeptide chain molecular weights of human and bovine band 3 proteins which are glycoproteins of the erythrocyte membrane were determined as 101,000 +/- 2000 for the former and 107,000 +/- 2000 for the latter by using the low-angle laser light scattering technique combined with a high-performance gel chromatography column, an ultraviolet spectrophotometer and a differential refractometer in the presence of sodium dodecyl sulfate. The advantage of this method is that, unlike the sedimentation equilibrium technique, neither information on the binding to proteins of all ligands present nor the partial specific volume is required to evaluate the polypeptide chain molecular weight of proteins in a multicomponent system.

Binding of chloride and a disulfonic stilbene transport inhibitor to red cell band 3

The effect of chloride on 4,4'-dibenzamido-2,2'-disulfonic stilbene (DBDS) binding to band 3 in unsealed red cell ghost membranes was studied in buffer [NaCl (0 to 500 mM) + Na citrate] at constant ionic strength (160 or 600 mM), pH 7.4, 25 degrees C. In the presence of chloride, DBDS binds to a single class of sites on band 3. At 160 mM ionic strength, the dissociation constant of DBDS increases linearly with chloride concentration in the range [Cl] = 10 to 120 mM; at 600 mM ionic strength, the DBDS dissociation constant saturates hyperbolically with half-saturating [Cl] = 450 mM. The observed rate of DBDS binding to ghost membranes, as measured by fluorescence stopped-flow kinetic experiments, increases with chloride concentration at both 160 and 600 mM ionic strength. The equilibrium and kinetic results have been incorporated into the following model of the DBDS-band 3 interaction: (formula; see text) The equilibrium and rate constants of the model at 600 mM ionic strength are K1 = 0.67 +/- 0.16 microM, k2 = 1.6 +/- 0.7 sec-1, k-2 = 0.17 +/- 0.09 sec-1, K'1 = 6.3 +/- 1.7 microM, k'2 = 9 +/- 4 sec-1 and k'-2 = 7 +/- 3 sec-1. The apparent dissociation constants of chloride from band 3, KCl, are 40 +/- 4 mM (160 mM ionic strength) and 11 +/- 3 mM (600 mM ionic strength). Our results indicate that chloride and DBDS have distinct, interacting binding sites on band 3.

The interaction of liposomes containing intrinsic erythrocyte membrane proteins with lipid monolayers at air/water and oil/water interfaces

The main intrinsic membrane proteins of the human erythrocyte membrane, glycophorin and the anion transporter, were isolated by extraction with Triton X-100 and ion-exchange chromatography. After removal of detergent the extract consisted of proteolipid vesicles with a lipid:protein molar ratio in the range 50-60 and a diameter of the order of 200 nm. The interaction between these vesicles and dipalmitoylphosphatidylcholine (DPPC), cholesterol and cholesterol:DPPC (2:1 molar ratio) monolayers at air/water and n-decane/water interfaces has been studied. The vesicles interact with the monolayers, rapidly causing large increases in surface pressure. Limiting values of surface pressure, 39.4-43 mN . m-1 at air/water and 31.5-33.4 mN . m-1 at the n-decane/water interface, were reached at protein levels above 1 microgram . ml-1. At the air/water interface, and probably at the n-decane/water, surface pressure increases were limited by monolayer collapse. Compression isotherms and surface potential measurements indicated that material from the proteolipid vesicles entered the monolayer phase. In contrast to proteolipid vesicles, injection of protein-free liposomes beneath the monolayer resulted in smaller, slower increases in surface pressure. Thus, the presence of intrinsic membrane proteins in vesicles greatly facilitated the transfer of material into the lipid monolayer.

A membrane protein in LRM55 glial cells cross-reacts with antibody to the anion exchange carrier of human erythrocytes

Cl-/HCO3-exchange transport in the glial plasma membrane is remarkably similar to anion exchange transport in erythrocytes. When LRM55 cells were pretreated with the extracellular labeling reagent [125I]iodosulfanilic acid, radioactivity appeared primarily in two bands on denaturing polyacrylamide gels at Mr 70,000 and 30,000. Antibody to the human erythrocyte anion exchanger (Band 3) cross-reacted on immunoblots with an LRM55 band at Mr 68,000. The LRM55 Cl-/HCO3-exchanger may be a component of Mr 68,000 to 70,000.

Predicted membrane topology of the coronavirus protein E1

The structure of the envelope protein E1 of two coronaviruses, mouse hepatitis virus strain A59 and infectious bronchitis virus, was analyzed by applying several theoretical methods to their amino acid sequence. The results of these analyses combined with earlier data on the orientation and protease sensitivity of E1 assembled in microsomal membranes lead to a topological model. According to this model, the protein is anchored in the lipid bilayer by three successive membrane-spanning helices present in its N-terminal half whereas the C-terminal part is thought to be associated with the membrane surface; these interactions with the membrane protect almost the complete polypeptide against protease digestion. In addition, it is predicted that the insertion of E1 into the membrane occurs by the recognition of the internal transmembrane region(s) as a signal sequence.

Improved preparation of the integral membrane proteins of human red cells, with special reference to the glucose transporter

Human red cell membranes were isolated and partially stripped of peripheral proteins by gel filtration of hemolysates on a Sepharose CL-4B column at pH 8 connected in tandem to a Sepharose CL-6B column at pH 10.5. The eluted material was washed by centrifugations, once at pH 10.5 and twice at pH 12. In this way, water-soluble proteins and peripheral membrane proteins were thoroughly removed, and 0.2 g of integral membrane proteins could be prepared within 10 h from 0.2 litre of red cells. The exposure to high pH did not lower the D-glucose transport activity, and electrophoretically pure glucose transport protein could be isolated from this preparation. Gel filtration in sodium dodecyl sulfate separated the integral membrane components into four fractions, one of them containing 4.5-material; gel electrophoresis showed about 14 zones and two-dimensional electrophoresis resolved up to 100 mostly minor components, among which the glucose transporter focused around pH 7. However, purified glucose transporter focused around pH 8. Glucose and nucleoside transport proteins were co-purified in active form on DEAE-cellulose and a fraction isolated by adsorption to Mono Q was used for immunization of mice and production of monoclonal antibodies. One hybridoma produced antibodies that reacted with material in the 4.5-region, possibly the glucose transport protein, and not with band 3-material. Upon two-dimensional electrophoresis of integral membrane components that had been solubilized with octyl glucoside the immunoreactive and the silver-stained 4.5-material focused in a broad range from pH 6 to pH 9. A possible explanation for this heterogeneity might be interaction between the glucose and nucleoside transport proteins and negatively charged lipids.

Virosome-mediated implantation of red cell band 3 into the plasma membrane of cultured hepatoma cells

A method for implanting exogenous membrane proteins into recipient hepatoma cells is described. Red cell band 3 and Sendai virus envelope proteins HN and F were extracted from their respective sources and purified by centrifugation to equilibrium through sucrose step gradients in the presence of octyl-beta-D-glucopyranoside. 0.05-0.15 micron vesicles were formed by adding lipid to combined detergent solubilized, isolated membrane proteins and removing detergent by dialysis. The vesicles were hybrid band 3-Sendai envelope vesicles and not a mixture of two distinct vesicle types as judged by (1) the ability of Sendai specific antibody to immunoprecipitate greater than 99% of band 3 from vesicle suspensions and (2) comigration of band 3 and Sendai envelope proteins on isopyknic sucrose density gradients. The hybrid vesicles (virosomes) were not fusogenic but did bind to cultured hepatoma cells in the cold. Subsequent treatment of virosomes absorbed onto cultured cells with polyethylene glycol resulted in a stable association of 2-10% of added band 3 and Sendai envelope proteins with the cells. Efficient transfer of virosome-associated band 3 to the cells was dependent on both lipid and Sendai envelope proteins. Fluid phase marker transfer, immunofluorescence, and protease digestion experiments demonstrate that the majority of the virosomes were implanted into recipient hepatoma membranes and not simply adsorbed onto their surface or immediately endocytosed. The hybrid membrane protein-viral envelope vesicles thus offer an efficient means for insertion of foreign proteins into the membranes of recipient cultured cells.

Structural characterization of the cytoplasmic pole of band 3 from bovine erythrocyte membranes

In an earlier study, we found that chymotryptic digestion of band 3 isolated from bovine erythrocyte membranes produces a 38,000-Da fragment in nonaethyleneglycol-n-dodecylether solution or a 50,000-Da fragment in deoxycholate solution as a primary fragment [Makino et al. (1984) J. Biochem. 95, 1019]. In the present study, these fragments were purified in an aqueous medium without detergent and their structural properties were examined. Several lines of evidence showed that the 50,000-Da fragment constitutes the entire cytoplasmic pole of bovine band 3 and that the 38,000-Da fragment is a subfragment of the 50,000-Da fragment. The large fragment was suggested to be divided into two distinct regions, the 12,000- and 38,000-Da portions, differing in their conformational thermal stability. However, attempts to identify the 12,000-Da portion as an isolable segment were without success. The cytoplasmic pole was characterized as a dimer which adopts an elongated gross conformation with helix of approximately 35%. Treatment of the fragments with dimethylmaleic anhydride dissociated the dimers into the monomers, accompanied by a significant conformational change of the 38,000-Da portion. Comparative studies suggested that the cytoplasmic domain of bovine band 3 has structurally different region(s) from that of human band 3, though their gross conformation shows extensive similarity.

Concentration dependence of the chloride selfexchange and homoexchange fluxes in human red cell ghosts

The concentration dependence of the unidirectional chloride flux in human red cell ghosts was studied under selfexchange and under homoexchange conditions. Under selfexchange conditions the intracellular concentration of chloride [Cl]in is equal to the extracellular concentration [Cl]ex and [Cl]in and [Cl]ex are raised concomitantly. Under homoexchange conditions [Cl]in or [Cl]ex were varied separately at a fixed trans-concentration of chloride. The chloride fluxes were calculated from the rate of the tracer efflux and the intracellular chloride. All experiments were executed in isotonic (330 mosM) KCl/K-citrate/sorbitol solutions containing 0-100 mM KCl, 40 mM K-citrate and different concentrations of sorbitol for isoosmotic substitution. The chloride selfexchange and the chloride homoexchange fluxes exhibit a pure saturation kinetics. The halfsaturation constant for the chloride selfexchange was approximately 20 mM, the maximal flux was approx. 3.5 X 10(-4) mol/(min . g cells). The apparent chloride halfsaturation constants from the homoexchange experiments were in the range of 0.9-4.5 mM for the outer and of 5.5-14.5 mM (0 degree C, pH 7.3) for the inner membrane surface, both halfsaturation constants increase with increasing trans-concentrations. At infinite trans-concentrations of chloride, the halfsaturation constant for the outer and the inner membrane surface amounts to approximately 5 mM and approximately 15 mM, respectively. The slope of the double reciprocal plots of flux versus cis-chloride concentration decreases with increasing trans-concentration of chloride. The kinetics of the chloride transport provides evidence for a carrier mediated transport mechanism with a single reciprocating transport site. The translocation of the loaded carrier appears to be much faster than the translocation of the unloaded carrier.(ABSTRACT TRUNCATED AT 250 WORDS)

Glyceraldehyde-3-phosphate dehydrogenase of rat erythrocytes has no membrane component

In the course of studying mammalian erythrocytes we noted prominent differences in the red cells of the rat. Analysis of ghosts by sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis showed that membranes of rat red cells were devoid of band 6 or the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (D-glyceraldehyde-3-phosphate: NAD+ oxidoreductase (phosphorylating), EC 1.2.1.12). Direct measurements of this enzyme showed that glyceraldehyde-3-phosphate dehydrogenase activity in rat erythrocytes was about 25% of that in human cells; all of the glyceraldehyde-3-phosphate dehydrogenase activity in rat erythrocytes was within the cytoplasm and none was membrane bound; and in the human red cell, about 1/3 of the enzyme activity was within the cytoplasm and 2/3 membrane bound. The release of glyceraldehyde-3-phosphate dehydrogenase from fresh rat erythrocytes immediately following saponin lysis was also determined using the rapid filtration technique recently described. The extrapolated zero-time intercepts of these reactions confirmed that, in the rat erythrocyte, none of the cellular glyceraldehyde-3-phosphate dehydrogenase was membrane bound. Failure of rat glyceraldehyde-3-phosphate dehydrogenase to bind to the membranes of the intact rat erythrocyte seems to be due to cytoplasmic metabolites which interact with the enzyme and render it incapable of binding to the membrane.

Anion transport in red blood cells and arginine-specific reagents. Interaction between the substrate-binding site and the binding site of arginine-specific reagents

Phenylglyoxal is found to be a potent inhibitor of sulfate equilibrium exchange across the red blood cell membrane at both pH 7.4 and 8.0. The inactivation exhibits pseudo-first-order kinetics with a reaction order close to one at both pH 7.4 and 8. The rate constant of inactivation at 37 degrees C was found to be 0.12 min-1 at pH 7.4 and 0.19 min-1 at pH 8.0. Saturation kinetics are observed if the pseudo-first order rate constant of inhibition is measured as a function of phenylglyoxal concentration. Sulfate ions as well as chloride ions markedly decrease the rate of inactivation by phenylglyoxal at pH 7.4, suggesting that the modification occurs at or near to the binding site for chloride and sulfate. The decrease of the rate of inactivation produced at pH 8.0 by chloride ions is much higher than that produced by sulfate ions. Kinetic analysis of the protection experiments showed that the loaded transport site is unable to react with phenylglyoxal. From the data it is concluded that the modified amino acid(s) residues, presumably arginine, is (are) important for the binding of the substrate anion.

Band 3 protein of the red cell membrane of the llama: crosslinking and cleavage of the cytoplasmic domain

Comparative studies were done on the cytoplasmic domain of the band 3 protein in the red cell membranes of the the human and the llama. Two approaches were used: crosslinking with o-phenanthroline/CuSO4, and cleavage with 2-nitro-5-thiocyanobenzoate. o-Phenanthroline/CuSO4 crosslinks the band 3 polypeptide chains in the human; in contrast band 3 in the llama is minimally crosslinked by this agent. 2-Nitro-5-thiocyanobenzoate cleaves band 3 in the human into a 23,000-dalton fragment; a similar fragment is not generated from the llama band 3. These studies show that the cysteine residue located 23,000 daltons from the N-terminus of band 3 in the human involved in these reactions is unavailable for crosslinking and cleavage in the llama. Species differences in the cytoplasmic domain of band 3 may contribute to the unusual resistance of llama red cells to osmotic, chemical and physically-induced deformation.

The role of hemoglobin denaturation and band 3 clustering in red blood cell aging

As hemoglobin begins to denature, it forms hemichromes that cross-link the major erythrocyte membrane-spanning protein, band 3, into clusters. These clusters provide the recognition site for antibodies directed against senescent cells. These antibodies bind to the aged red cell and trigger its removal from circulation.

Adsorption of peripheral enzymes to membrane anchor proteins

The character of the isotherms of specific adsorption of peripheral enzymes to dimeric anchor proteins embedded in the membrane has been analysed. The situations are discussed when adsorption corresponds to the stoichiometry of one or two molecules of peripheral enzyme per dimeric binding site. The corresponding expressions describing the competitive interrelationships between peripheral enzymes adsorbed to the same binding sites have been derived. The experimental data on the adsorption of glycolytic enzymes to erythrocyte membranes are used for the illustration of the theoretical predictions. The physiological role of enzyme self-association which leads to the formation of enzyme oligomers of unlimited length is discussed. It is assumed that under in vivo conditions the association sites of such enzymes are saturated through interactions with anchor proteins of subcellular structures and with the enzymes of the corresponding metabolic pathways. Therefore the linearly associating enzymes play the key role in the formation of multienzyme complexes attached to subcellular structures. The significance of 6-phosphofructokinase adsorption to erythrocyte membranes in the formation of the complex of glycolytic enzymes is discussed.

Fractionation of human red cell membrane proteins by ion-exchange chromatography in detergent on Mono Q, with special reference to the glucose transporter

The anion exchanger Mono Q has been used for rapid and efficient fractionation of human red cell membrane proteins in the easily removable detergents n-octyl-beta-D-glucopyranoside or nonanoyl-N-methylglucamide. In practice the chromatographic resolution of membrane proteins was lower than for water-soluble proteins, perhaps due to protein-protein interactions and microheterogeneity, but several components, or groups of components, separated well upon salt gradient elution. The glucose transporter (or transportase) was eluted early, glycophorins later, and the anion transporter still later. The detergents Berol 185 and the zwitter-ionic derivatives of cholate, 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulphonat e and 3-[(3-cholamidopropyl)dimethylammonio]-2-hydroxy-1-propan esulphonate, gave similar chromatographic results but differed in solubilization selectivity. A relatively pure material was also fractionated; viz., a glucose transportase which had been prepared by DEAE-cellulose chromatography. Mono Q, in the presence of octyl glucoside, afforded additional purification, which made automatic sequence determination possible for eighteen amino acid residues. The results indicate that two polypeptides were present in about equimolar amounts.

Organic phosphates modulate anion self-exchange across the human erythrocyte membrane

Anion transport across the red cell membrane has been measured as sulfate self-exchange flux (Ja) in fresh and metabolically depleted human red cells. Depletion of metabolic stores by a starvation of the cells decreases Ja by 50%. A similar effect was observed when ATP was acutely and selectively depleted by iodoacetamide. This inhibition was independent of the presence of calcium and reversible after metabolic rejuvenation of the cells. Ghosts prepared from fresh red cells exhibited the same value of Ja as fresh red cells. By contrast, ghosts prepared from depleted red cells exhibited a decrease in Ja which was reverted by a physiological concentration of ATP. The effect of ATP was dependent on its concentration (Km approximately 40 microM) and on the duration of the metabolic depletion: complete restoration of Ja was obtained only in ghosts prepared from red cells acutely depleted of ATP by a 2 h incubation with iodoacetamide. After a 20 h starvation, Ja restoration was never more than 80%. We postulate that ATP acts primarily through the phosphorylation of band 3 protein, the anion exchanger; it acts also through the stabilization of the normal organization of the membrane. This latter effect may involve the phosphorylation of membrane components, but also a direct interaction, as shown by the influence of other organic phosphates (2,3-diphosphoglycerate and inositol hexaphosphate) on Ja in the absence of ATP.