The carboxyl-terminal domain of human erythrocyte band 3. Description, isolation, and location in the bilayer

Topological disposition of tyrosine 486 in anion exchanger from human erythrocytes

The location with respect to the plasma membrane of tyrosine 486 in the native anion exchanger of human erythrocytes has been determined by site-directed immunochemistry. Intact erythrocytes and inside-out vesicles were [125I]radioiodinated by lactoperoxidase in the same vessel. After the erythrocytes and inside-out vesicles had been separated by differential centrifugation, the modified polypeptide of the anion exchanger was isolated from each sample and digested with the proteinase from Staphylococcus aureus strain V8 and trypsin to generate the peptide YIVGR. An immunoadsorbent that was specific for the carboxy-terminal sequence -IVGR was used to purify the peptide YIVGR, which contains tyrosine 486 of the anion exchanger, from the products of the digestion. The [125I]radioiodinated peptides isolated by the immunoadsorbent were submitted to high-pressure liquid chromatography, and their respective mobilities were compared to those of synthetic peptides that had been iodinated at tyrosine. By applying this technique, the peptide containing tyrosine 486 was unambiguously identified, and the incorporation of [125I]iodine into this residue in anion exchanger could be monitored. When inside-out vesicles and intact cells were [125I]radioiodinated in the same suspension, tyrosine 486 was modified to at least a 6-fold greater specific radioactivity in the inside-out vesicles than it was in the intact cells. This amino acid, therefore, was assigned to the cytoplasmic surface of native anion exchanger. It follows that the polypeptide of anion exchanger spans the membrane three times before it reaches the extracellular region surrounding glutamine 550.

Antibodies to synthetic peptides based on band 3 motifs react specifically with Plasmodium falciparum (human malaria)-infected erythrocytes and block cytoadherence

Rabbit polyclonal and mouse monoclonal antibodies (Mabs) prepared against synthetic peptides patterned on exofacial loops 3 (amino acids 546-555) and 7 (821-834) of the human anion transport protein band 3 inhibited the cytoadherence of Plasmodium falciparum-infected erythrocytes to C32 amelanotic melanoma cells. Mabs directed against exofacial loop 4 (amino acids 628-642) did not inhibit adherence to a significant degree. The murine Mabs recognized only P. falciparum-infected cryptic in uninfected erythrocytes.

Cytoadherence-related neoantigens on Plasmodium falciparum (human malaria)-infected human erythrocytes result from the exposure of normally cryptic regions of the band 3 protein

Murine monoclonal antibodies (Mabs) were produced by vaccination of Balb/c mice with live Plasmodium falciparum-infected red cells (iRBC). The iRBC Mabs recognized altered forms of the human erythrocyte membrane protein band 3; however, these Mabs did not recognize the band 3 molecule in uninfected or ring-infected red cells. The location of epitopes was determined by studying the binding of the iRBC Mabs after selective proteolysis of band 3 as well as by the reactivity of these Mabs to synthetic peptides that corresponded to putative exofacial regions of band 3. Treatment of uninfected red cell membranes with trypsin under low ionic strength conditions resulted in exposure of cryptic epitopes of band 3 which were recognized by the iRBC Mabs. Several of the anti-iRBC Mabs (two of which were described previously) inhibited the in vitro adherence of infected erythrocytes to C32 amelanotic melanoma cells. A mouse polyclonal serum against a synthetic peptide based on an amino acid sequence motif of band 3 reacted (by immunostaining) only with the surface of iRBC and blocked adhesion. Thus, it appears that cryptic residues of the band 3 protein become exposed upon parasitization, and their presence contributes to the increased adhesiveness of the P. falciparum-infected red cell.

Naturally occurring anti-band 3 autoantibodies recognize a high molecular weight protein on the surface of Plasmodium falciparum infected erythrocytes

Naturally occurring anti-band 3 autoantibodies bind to erythrocytes infected with a knobby variant of the human malaria Plasmodium falciparum (FCR-3 strain). The autoantibodies recognized a greater than 240 kDa protein in SDS extracts made from surface iodinated infected erythrocytes. The antigen was associated only with erythrocytes infected with a knobby variant, and was removed by trypsin treatment of intact infected cells. By two-dimensional peptide map analysis the antigen was shown to be structurally related to the human erythrocyte anion transporter, band 3.

Secondary structure and assembly mechanism of an oligomeric channel protein

The alpha-toxin of Staphylococcus aureus is secreted as a water-soluble, monomeric polypeptide (Mr 33 182) that can assemble into an oligomeric membrane channel. By chemical cross-linking, we have confirmed that the major form of the channel is a hexamer. The circular dichroism spectrum of this hexamer in detergent revealed that it contains a high proportion of beta-sheet that we deduce must lie within the lipid bilayer when the protein is associated with membranes. The circular dichroism spectrum of the monomeric toxin in the presence or absence of detergent was closely similar to the spectrum of the hexamer, suggesting that the secondary structure of the polypeptide is little changed on assembly. Results of experiments involving limited proteolysis of the monomer and hexamer are consistent with the idea that assembly involves the movement of two rigid domains about a hinge located near the midpoint of the polypeptide chain. The hydrophilic monomer is thereby converted to an amphipathic rod that becomes a subunit of the hexamer.

Human erythrocyte membrane proteins of zone 4.5 exist as families of related proteins

An analysis of the polypeptide composition of zone 4.5 of human erythrocyte membranes has been done by immunoautoradiographic and two-dimensional peptide mapping techniques. Results of these studies demonstrated that the Coomassie blue profile was constant, with 14 well-resolved bands present. Zone 4.5 polypeptides existed as at least four families of two or more components with closely related polypeptide backbones. The families could be distinguished on the basis of their extraction characteristics, immunological cross-reactivity, and two-dimensional peptide maps. One family was related to protein 4.1, one family was related to band 3, and two families were independent and not similar to other larger membrane proteins. The data show that all of the visualized bands in zone 4.5 do not have the same protein composition and that several closely related forms of some polypeptides are present.

The preparation of hydrophilic derivatives of band 3 protein by acylation of the human red blood cell membrane

In situ reaction of erythrocyte membranes with dicarboxylic anhydrides leads to solubilization of hydrophobic integral proteins. Removal of peripheral proteins and bulk lipid by appropriate sedimentation and dialysis steps yields hydrophilic band 3 protein derivatives. These acyl compounds display size heterogeneity upon gel filtration. A chromatographically homogeneous acyl band 3 protein is obtained if the acylation is conducted in the presence of detergent and the detergent subsequently removed. Hydrophilic acyl derivatives of band 3 protein can be subjected to conventional analytical techniques without the use of detergents.

Phospholipid dependence of the anion transport system of the human erythrocyte membrane. Studies on reconstituted band 3/lipid vesicles

Band 3 protein extracted from human erythrocyte membranes by Triton X-100 was recombined with the major classes of phospholipid occurring in the erythrocyte membrane. The resulting vesicle systems were characterized with respect to recoveries, phospholipid composition, protein content and vesicle size as well as capacity and activation energy of sulfate transport. Transport was classified into band-3-specific fluxes and unspecific permeability by inhibitors. Transport number (sulfate ions per band 3 per minute) served as a measure of functional therapy after reconstitution. The transport properties of band 3 proved to be insensitive to replacement of phosphatidylcholine by phosphatidylethanolamine, while sphingomyelin and phosphatidylserine gradually inactivated band-3-specific anion transport when present at mole fractions exceeding 30 mol%. The activation energy of transport remained unaltered in spite of the decrease in transport numbers. The results, which are discussed in terms of requirements of band 3 protein function with respect to the fluidity and surface charge of its lipid environment, provide a new piece of evidence that the transport function of band 3 protein depends on the properties of its lipid environment just as the catalytic properties of some other membrane enzymes. The well-established species differences in anion transport (Gruber, W. and Deuticke, B. (1973) J. Membrane Biol. 13, 19-36) may to some extent reflect this lipid dependence.

Characterization and identification of the glucose transporter of human erythrocytes

The glucose transporter was purified from human erythrocytes (Kasahara, M. and Hinkle, P.C. (1977) J. Biol. Chem. 252, 7384-7390). The following results support the conclusion that a major protein in the purified transporter fraction, zone 4.5 is the glucose transporter (or a part of the transporter) and is different from band 3: (1) peptide maps of zone 4.5 were similar throughout the broad band in sodium dodecyl sulfate-gel electrophoresis and were different from those of band 3, (2) specific binding of cytochalasin B was found to the transporter fraction, but not to a band 3 fraction, (3) the N-terminal amino acid analysis of the transporter fraction showed a single N-terminal of lysine, whereas the band 3 fraction showed no clear N-terminal, and (4) the rabbit antibody raised against the transporter fraction formed a precipitation line with the transporter fraction, but not with the band 3 fraction. A filtration apparatus was devised for quick and accurate measurement of cytochalasin B binding, with which results comparable to those from equilibrium dialysis were obtained.

Heterogeneity of human erythrocyte band 3 analyzed by two-dimensional gel electrophoresis

Human erythrocyte membrane and purified band 3 were separated initially by isoelectric focusing and then examined in a second dimension by sodium dodecyl sulfate/polyacrylamide gel electrophoresis. Band 3 was segregated into three major bands whether the protein was contained within the membranes or was present in the isolated state. The isoelectric points of these major bands were 5.25, 5.35 and 5.70. Of chymotryptic fragments of band 3, the 60-kDa fragment was also separated into three major bands whose pI values were 4.75, 5.10 and 5.30. The multiplicity of band 3 appears to be due to different charges carried by the peptide(s) and is not ascribed to oxidation of band 3 during its preparation. Isoelectric points of the purified 60-kDa fragment were different from the pI values of the fragment coexisting with the complementary 35-kDa fragment, in which case the pI values were exactly the same as those of intact band 3. This suggests that these fragments interact tightly in situ even after being cleaved by chymotrypsin, and the tight interaction must still be present during electrophoresis in the first dimension.

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.