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R A Reithmeier

Publications and source records attributed to R A Reithmeier.

At least 55 records · Page 3Linked to original sources
PubMed1992

Enzymatic deglycosylation of human Band 3, the anion transport protein of the erythrocyte membrane. Effect on protein structure and transport properties.

The structural and functional roles of the single asparagine (N)-linked oligosaccharide chain of Band 3 (AE1), the anion transport protein of the human erythrocyte membrane, were examined. Purified Band 3 (M(r) = 95,000) in 0.1% octaethylene glycol mono n-dodecyl ether (C12E8) detergent solution was deglycosylated using N-glycosidase F. This treatment sharpened the protein band on sodium dodecyl sulfate gel electrophoresis and decreased its apparent molecular weight by 5,000. The purified membrane domain could be deglycosylated under similar conditions, causing a shift from a broad band centered at 55 kDa to a sharp 46-kDa band. Band 3 was shown to bind tomato lectin, and loss of lectin binding on blots provided a sensitive assay for deglycosylation. Carbohydrate analysis revealed that greater than 80% of the oligosaccharide could be removed from Band 3 by N-glycosidase F digestion. The deglycosylated protein maintained its dimeric structure and level of detergent binding but had a smaller Stokes radius (RS = 72 A) than native Band 3 (RS = 75 A). The Stokes radius of the membrane domain (RS = 60 A) also decreased upon deglycosylation (RS = 58 A). Circular dichroism studies showed that deglycosylation did not change the secondary structure of Band 3 or the membrane domain. The sensitivity of Band 3 or the membrane domain to proteolytic digestion by trypsin or proteinase K was also unaffected by deglycosylation. The deglycosylated protein aggregated more rapidly and was much more readily precipitable by ammonium sulfate. The deglycosylated protein bound the anion transport inhibitor 4-benzamido-4'-amino-stilbene-2,2'-disulfonate with the same affinity (Kd = 1 microM) as the native protein. Transport studies using reconstituted Band 3 and resealed ghosts showed that deglycosylated Band 3 retained its ability to transport anions. We conclude that removal of the oligosaccharide chain from Band 3 and any resultant structural changes had no effect on the transport function of this protein.

Anion Exchange Protein 1, Erythrocyte↗
PubMed1991

Analysis of the oligomeric state of Band 3, the anion transport protein of the human erythrocyte membrane, by size exclusion high performance liquid chromatography. Oligomeric stability and origin of heterogeneity.

The oligomeric state of human Band 3 (Mr = 95,000), the erythrocyte membrane anion exchanger, was examined by size exclusion high performance liquid chromatography in solutions containing the nonionic detergent C12E8 (octaethylene glycol n-dodecyl monoether). Band 3 was heterogeneous with respect to oligomeric composition, the predominant (70%) species being a dimer that bound 0.57 mg of C12E8/mg of protein (Stokes radius = 78 A, s20,w = 6.9 S). Variable amounts of larger oligomers were also present; however, no evidence for equilibration between oligomeric species was observed in detergent solution. Analytical and large zone size exclusion chromatography showed that Band 3 could not be dissociated to monomers, other than by protein denaturation. The membrane domain of Band 3 (Mr = 52,000) was also dimeric, but without evidence for higher oligomeric forms, which implies that the interactions responsible for higher associations involve the cytoplasmic domain. Prelabeling of Band 3 with the anion exchange inhibitor 4,4'-diisothiocyanostilbene-2,2'-disulfonate had no effect upon the oligomeric state of either intact Band 3 or its 52-kDa membrane domain. Band 3 oligomeric state could be reversibly changed in the membrane by altering the pH of the solution. The fraction of Band 3 not associated with the cytoskeleton was almost entirely dimeric. Band 3 purified from erythrocytes separated by density gradient centrifugation revealed that older red cells contained a larger proportion of higher oligomers than did younger cells. We conclude that Band 3, in the membrane and in C12E8 solution, exists as a mixture of dimers and larger oligomers. The higher oligomers interact with the cytoskeleton, increase in amount with cell age, and are held together by interactions of the cytoplasmic domain.

Anion Exchange Protein 1, Erythrocyte↗
PubMed1990

Identification and characterization of the major stilbene-disulphonate- and concanavalin A-binding protein of the porcine renal brush-border membrane as aminopeptidase N.

A 130 kDa glycoprotein (GP 130) was purified from porcine renal brush-border membranes by affinity chromatography using immobilized 4-acetamido-4'-isothiocyanostilbene-2,2'-disulphonate (SITS)- and concanavalin A-Sepharose. GP 130 was the major concanavalin A-binding protein in porcine renal brush-border membranes and also bound Ricinus communis (castor-bean) and wheat-germ agglutinins. Endo-beta-N-acetylglucosaminidase F reduced the molecular mass of GP 130 by 20 kDa as determined by SDS/PAGE, whereas endo-beta-N-acetylglucosaminidase H reduced the molecular mass by 5 kDa, showing that GP 130 contained both complex and high-mannose carbohydrate structures. Western-blot analyses using an antibody raised against GP 130 showed that it was localized to the brush-border membrane fraction and was present in a membrane fraction of the pig kidney cell line LLC-PK1. The N-terminal sequence and amino acid composition of GP 130 showed that GP 130 is similar to rat kidney zinc peptidase and human intestinal aminopeptidase N. GP 130 had aminopeptidase N enzymic activity and was inhibited by bestatin (Ki = 36 microM), 1,10-phenanthroline (Ki 30 microM), Zn2+ (Ki 26 microM), Cu2+ (Ki 260 microM), pre-incubation with EDTA and by a polyclonal antibody against GP 130. Bicarbonate and iodide blocked the binding of GP 130 to the SITS-affinity resin, showing that GP 130 has an anion-binding site. Neither these anions nor stilbene disulphonates affected the aminopeptidase N activity of GP 130.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1990

Interaction of ruthenium red with Ca2(+)-binding proteins.

The interaction of ruthenium red, [(NH3)5Ru-O-Ru(NH3)4-O-Ru(NH3)5]Cl6.4H2O, with various Ca2(+)-binding proteins was studied. Ruthenium red inhibited Ca2+ binding to the sarcoplasmic reticulum protein, calsequestrin, immobilized on Sepharose 4B. Furthermore, ruthenium red bound to calsequestrin with high affinity (Kd = 0.7 microM; Bmax = 218 nmol/mg protein). The dye stained calsequestrin in sodium dodecyl sulfate-polyacrylamide gels or on nitrocellulose paper and was displaced by Ca2+ (Ki = 1.4 mM). The specificity of ruthenium red staining of several Ca2(+)-binding proteins was investigated by comparison with two other detection methods, 45Ca2+ autoradiography and the Stains-all reaction. Ruthenium red bound to the same proteins detected by the 45Ca2+ overlay technique. Ruthenium red stained both the erythrocyte Band 3 anion transporter and the Ca2(+)-ATPase of skeletal muscle sarcoplasmic reticulum. Ruthenium red also stained the EF hand conformation Ca2(+)-binding proteins, calmodulin, troponin C, and S-100. This inorganic dye provides a simple, rapid method for detecting various types of Ca2(+)-binding proteins following electrophoresis.

Animals↗
PubMed1989

Molecular cloning of the high affinity calcium-binding protein (calreticulin) of skeletal muscle sarcoplasmic reticulum.

A cDNA clone encoding the high affinity Ca2+-binding protein (HACBP) of rabbit skeletal muscle sarcoplasmic reticulum was isolated and sequenced. The cDNA encoded a protein of 418 amino acids, but a comparison of the deduced amino acid sequence with the NH2-terminal amino acid sequence of the purified protein indicates that a 17-residue NH2-terminal signal sequence was removed during synthesis. This was confirmed by studies of in vitro translation of mRNA encoding the protein. Structural predictions did not reveal any potential transmembrane segments in the protein. The COOH-terminal sequence of the high affinity Ca2+-binding protein, Lys-Asp-Glu-Leu, is the same as that proposed to be an endoplasmic reticulum retention signal (Munro, S., and Pelham, H. R. B. (1987) Cell 48, 899-907). All of these characteristics suggest that the protein is localized in the lumen of the sarcoplasmic reticulum. The mature protein of Mr 46,567 contains 109 acidic and 52 basic amino acids. Structural predictions suggest that the first half of the molecule forms a globular domain of 8 anti-parallel beta-strands with a helix-turn-helix motif at the extreme NH2 terminus. The next one-third of the sequence is proline-rich. This segment can be subdivided into a charged region which contains a 17-amino acid repeat, followed by a proline, serine, and threonine-rich segment extending from Pro-246 to Thr-316. Thirty-seven acidic residues are clustered within 56 amino acids at the COOH terminus of the protein. Although the protein binds 1 mol of Ca2+/mol with high affinity, no "EF-hand" consensus sequence was observed in the protein. The acidic COOH terminus, however, could account for the low affinity, high capacity Ca2+ binding observed in the protein. In agreement with other involved laboratories, we have chosen the name calreticulin for the protein.

Amino Acid Sequence↗
PubMed1989

Identification of P-glycoprotein in renal brush border membranes.

A monoclonal antibody (C219) that recognizes the P-glycoprotein (Mr = 170,000) in plasma membranes of multidrug-resistant Chinese hamster ovary (CHO) cell lines was used to assay renal brush border membrane (BBM) and basolateral membrane (BLM) fractions for the presence of a cross-reactive polypeptide. The C219 antibody bound to a 155,000 dalton protein in immunoblots of rat BBM but not BLM proteins resolved by sodium dodecyl sulfate gel electrophoresis. The corresponding human kidney BBM and dog kidney BBM proteins had molecular weights of 170,000 and 160,000 respectively. The glycoprotein nature of the renal protein was shown by its sensitivity to N-glycanase treatment which reduced the apparent molecular weight of the dog protein to 120,000. In addition, dog P-glycoprotein could be bound to and eluted from immobilized wheat germ agglutinin. The molecular weight, antibody crossreactivity, glycosidase sensitivity and lectin binding show that this protein is a normal kidney analogue of the P-glycoprotein induced in multidrug resistant cell lines.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1989

Accessibility of the N-ethylmaleimide-unreactive sulfhydryl of human erythrocyte Band 3.

The human erythrocyte anion exchange protein, Band 3, was reacted with N-ethylmaleimide (NEM) in cells to a stoichiometry of 5.3 mol NEM per mol Band 3, indicating that all NEM-reactive cysteines in Band 3 were labeled. Quantitatively NEM-blocked Band 3 was still able to bind to and be eluted by reducing agents from a mercurial affinity resin, [p-(chloromercuribenzamido)ethylene]amino-Sepharose. Reaction of NEM-blocked Band 3 with p-chloromercuribenzoate (pCMB) did not prevent binding to the resin due to exchange of pCMB for the immobilized mercurial. pCMB has been reported to inhibit water and urea permeation across the red cell membrane, and this has been attributed to reaction with a NEM-reactive sulfhydryl in Band 3. The interaction of Band 3 with the immobilized ligand directly demonstrates the reaction of NEM-blocked Band 3 with a mercurial and indicates that the NEM-unreactive, pCMB-reactive sulfhydryl residue is accessible to within approximately equal to 12 A (the distance from the solid support to the Hg) of the surface of the solubilized Band 3 protein.

Anion Exchange Protein 1, Erythrocyte↗
PubMed1988

Studies on the interaction of matrix-bound inhibitor with Band 3, the anion transport protein of human erythrocyte membranes.

The effect of temperature and chemical modification on the interaction of the human erythrocyte Band 3 protein (the anion transport protein) with 4-acetamido-4'-isothiocyanostilbene 2,2'-disulfonate (SITS; Ki = 10 microM)-Affi-Gel 102 resin was studied. Band 3 binds to the affinity resin in two states; weakly bound, which is eluted by 1 mM 4-benzamido-4'-aminostilbene 2,2'-disulfonate (BADS; Ki = 2 microM), and strongly bound, which is eluted only under denaturing conditions by 1% lithium dodecyl sulfate (LDS). At 4 degrees C, most of band 3 was present initially in the weakly bound form and very little in the strongly bound form. With longer incubations at 4 degrees C, the weakly bound form was slowly converted to the strongly bound form. At 37 degrees C, most of Band 3 was rapidly converted to the strongly bound form, with some Band 3 still remaining in the weakly bound form. Band 3 dimers, labelled with 4,4'-diisothiocyanostilbene 2,2'-disulfonate (DIDS) in one monomer, did bind to immobilized SITS but did not become tightly bound upon incubation at 37 degrees C. Since the covalent attachment of DIDS to one monomer prevented the adjacent monomer from becoming tightly bound to immobilized SITS ligand, this observation suggests that the inhibitor-binding sites of the two adjacent monomers must be interacting with each other. When the inhibitor site of Band 3 was selectively modified by citrate in the presence of 1-ethyl-3-(3-azonia-4,4-dimethylpentyl)carbodiimide (EAC), Band 3 bound to the resin was more easily eluted by BADS, suggesting reduced affinity for immobilized SITS. However, citrate-modified Band 3 did become tightly bound upon incubation at 37 degrees C.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1988

Localization of the carboxyl terminus of Band 3 to the cytoplasmic side of the erythrocyte membrane using antibodies raised against a synthetic peptide.

Polyclonal antibodies were raised in rabbits against a synthetic peptide which corresponds to the 12-amino acid carboxyl-terminal sequence of murine erythrocyte Band 3. Immunoblots of ghost membrane proteins showed that the antibody specifically recognized murine or rat Band 3 but not human or canine Band 3. The antibody also bound to murine ghost membranes applied directly to nitrocellulose but not to human ghost membranes. This shows that the carboxyl terminus of Band 3 is available for antibody binding in ghost membranes and that the carboxyl-terminal sequences of human and mouse Band 3 are not identical. The specificity of the antibody for the carboxyl terminus of Band 3 was confirmed by the loss of antibody binding after digestion of detergent-solubilized ghost membrane proteins with carboxypeptidase Y. In addition, carboxyl-terminal fragments of Band 3 generated by protease treatment of cells or ghost membranes were positive on immunoblots while amino-terminal fragments were negative. In contrast, protease-treated stripped ghost membranes did not contain a carboxyl-terminal fragment of Band 3 that was detectable on immunoblots. The carboxyl terminus of Band 3 was localized to the cytoplasmic side of the erythrocyte membrane since antibody binding as determined by immunofluorescence occurred in ghosts and permeabilized cells but not in intact cells. In addition, competition studies using enzyme-linked immunosorbent assays and immunoblots showed that cells and resealed ghosts competed poorly for antibody compared to ghost membranes, inside-out vesicles, or albumin-conjugated peptide.

Amino Acid Sequence↗
PubMed1988

The mechanisms of inhibition of anion exchange in human erythrocytes by 1-ethyl-3-[3-(trimethylammonio)propyl]carbodiimide.

Treatment of human erythrocytes with the membrane-impermeant carbodiimide 1-ethyl-3-[3-(trimethylammonio)propyl]carbodiimide (ETC) in citrate-buffered sucrose leads to irreversible inhibition of phosphate-chloride exchange. The level of transport inhibition produced was dependent on the concentration of citrate present during treatment, with a maximum of approx. 60% inhibition. [14C]Citric acid was incorporated into Band 3 (Mr = 95,000) in proportion to the level of transport inhibition, reaching a maximum stoichiometry of 0.7 mol citrate per mol Band 3. The citrate label was localized to a 17 kDa transmembrane fragment of the Band 3 polypeptide. Citrate incorporation was prevented by the transport inhibitors 4,4'-diisothiocyano- and 4,4'-dinitrostilbene-2,2'-disulfonate. ETC plus citrate treatment also dramatically reduced the covalent labeling of Band 3 by [3H]4,4'-diisothiocyano-2,2'-dihydrostilbene disulfonate (3H2DIDS). Noncovalent binding of stilbene disulfonates to modified Band 3 was retained, but with reduced affinity. We propose that the inhibition of anion exchange in this case is due to carbodiimide-activated citrate modification of a lysine residue in the stilbenedisulfonate binding site, forming a citrate-lysine adduct that has altered transport function. The evidence is consistent with the hypothesis that the modified residue may be Lys a, the lysine residue involved in the covalent reaction with H2DIDS. Treatment of erythrocytes with ETC in the absence of citrate resulted in inhibition of anion exchange that reversed upon prolonged incubation. This reversal was prevented by treatment in the presence of hydrophobic nucleophiles, including phenylalanine ethyl ester. Thus, inhibition of anion exchange by ETC in the absence of citrate appears to involve modification of a protein carboxyl residue(s) such that both the carbodiimide- and the nucleophile-adduct result in inhibition.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1988

Identification, purification, and characterization of a stilbenedisulfonate binding glycoprotein from canine kidney brush border membranes. A candidate for a renal anion exchanger.

Canine renal brush border membrane proteins that bind stilbenedisulfonate inhibitors of anion exchange were identified by affinity chromatography. A 130-kDa integral membrane glycoprotein from brush border membrane was shown to bind specifically to 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonate immobilized on Affi-Gel 102 resin. The bound protein could be eluted effectively with 1 mM 4-benzamido-4'-aminostilbene-2,2'-disulfonate (BADS). The 130-kDa protein did not bind to the affinity resin in the presence of 1 mM BADS or when the solubilized extract was covalently labeled with 4,4'-diisothiocyanostilbene-2,2'-disulfonate (DIDS). This protein was labeled with [3H]H2DIDS, and the labeling was prevented by BADS. The 130-kDa protein did not cross-react with antibody raised against human or dog erythrocyte Band 3 protein. The 130-kDa protein was accessible to proteinase K and chymotrypsin digestion in vesicles but not to trypsin. The 130-kDa protein was sensitive to endo-beta-N-acetylglucosaminidase F treatment both in the solubilized state and in brush border membrane vesicles showing that it was a glycoprotein and that the carbohydrate was on the exterior of the vesicles. This glycoprotein was resistant to endo-beta-N-acetylglucosaminidase H treatment suggesting a complex-type carbohydrate structure. The protein bound concanavalin A, wheat germ agglutinin, and Ricinus communis lectins, and it could be purified using wheat germ agglutinin-agarose.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1987

Fragmentation of rabbit skeletal muscle calsequestrin: spectral and ion binding properties of the carboxyl-terminal region.

Rabbit skeletal muscle calsequestrin was fragmented by using trypsin in the presence and absence of calcium. Calcium ion was found to protect calsequestrin from proteolysis, and the peptides produced in the presence of calcium were stable to further digestion. Peptides produced in the presence or absence of calcium had a decreased helical content but maintained their ability to bind calcium. The amino acid sequence of a 59-residue carboxyl-terminal tryptic peptide was determined by automated Edman degradation and carboxypeptidase Y digestion of carboxyl-terminal tryptic, chymotryptic, and cyanogen bromide peptides. This peptide is highly acidic (Asp + Glu = 42%, Lys + Arg = 0), and it bound a total of 15 calcium ions per mole of peptide (Kd = 8.5 mM). The intrinsic tryptophan fluorescence of the peptide was enhanced by 10% upon binding Ca2+ with the dissociation constant of 1 mM. Analyses of the circular dichroism spectra of the peptide showed that it was primarily in a random-coil conformation with little helical (2%) and moderate beta-structure (25%) regardless of the calcium concentration. This peptide also bound 7 mol of terbium per mole of peptide with high affinity (Kd = 7.5 microM).

Amino Acid Sequence↗
PubMed1987

Characterization of cardiac calsequestrin.

Calsequestrin, a calcium-binding protein found in the sarcoplasmic reticulum of muscle cells, was purified from rabbit and canine cardiac and skeletal muscle tissue. The amino acid compositions and amino-terminal sequences of skeletal and cardiac calsequestrin from rabbit and dog were determined. The amino acid composition of the cardiac form was very similar to the skeletal form. The amino-terminal sequence of the cardiac form was homologous to, but not identical with, the amino-terminal sequence of the skeletal form of the protein. Few species differences in the amino-terminal sequences were observed. The calcium-binding capacity of the cardiac form was half the capacity of the skeletal form although the affinities of the two forms of calsequestrin for Ca2+ were similar (Kd = 1 mM). Calcium binding to the cardiac form induced structural changes in the protein as determined by circular dichroism and intrinsic fluorescence spectroscopy. The alpha-helical content of cardiac calsequestrin increased from 3.5% to 10.9% upon binding calcium, while the intrinsic fluorescence of the protein increased 14%. Potassium ions also affected the conformation of cardiac calsequestrin.

Amino Acid Sequence↗
PubMed1987

Terbium-binding properties of calsequestrin from skeletal muscle sarcoplasmic reticulum.

Calsequestrin (Mr = 40,000) is a calcium-binding protein (Kd = 1 mM, 50 sites/molecule) located within the terminal cisternae of the sarcoplasmic reticulum of skeletal muscle cells. The interaction of terbium, a calcium analog, with rabbit skeletal muscle calsequestrin was studied by fluorescence and circular dichroism spectroscopy. Direct measurement of terbium binding using a fluorescence assay for terbium revealed that calsequestrin bound approx. 30 mol of terbium per mol of protein with an affinity of approx. 7 microM. The fluorescence of terbium measured at 545 nm was enhanced dramatically upon binding to calsequestrin, reaching a maximum value at a terbium to protein ratio of 28. The excitation spectrum of protein-bound terbium and chemical modification studies revealed that energy transfer occurred between aromatic residues, including tryptophan and bound terbium. Terbium bound to calsequestrin could be removed by EGTA, or displaced by Ca2+ or La3+. In the presence of Ca2+ or La3+ terbium bound to calsequestrin with a higher apparent affinity and lower capacity. 0.1 M KCl or 5 mM MgCl2 had little effect on terbium binding. Terbium increased the intrinsic fluorescence of calsequestrin 2-fold, and increased the alpha-helical content of calsequestrin from 16 to 33%. Terbium binding induces the same conformational changes in calsequestrin as does calcium, confirming that terbium is a useful calcium analog in this system.

Animals↗
PubMed1987

Carboxypeptidase Y digestion of band 3, the anion transport protein of human erythrocyte membranes.

The exposure of the carboxyl-terminal of the Band 3 protein of human erythrocyte membranes in intact cells and membrane preparations to proteolytic digestion was determined. Carboxypeptidase Y digestion of purified Band 3 in the presence of non-ionic detergent released amino acids from the carboxyl-terminal of Band 3. The release of amino acids was very pH dependent, digestion being most extensive at pH 3, with limited digestion at pH 6 or above. The 55,000 dalton carboxyl-terminal fragment of Band 3, generated by mild trypsin digestion of ghost membranes, had the same carboxyl-terminal sequence as intact Band 3, based on carboxypeptidase Y digestion. Treatment of intact cells with trypsin or carboxypeptidase Y did not release any amino acids from the carboxyl-terminal of Band 3. In contrast, carboxypeptidase Y readily digested the carboxyl-terminal of Band 3 in ghosts that were stripped of extrinsic membrane proteins by alkali or high salt. This was shown by a decrease in the molecular weight of a carboxyl-terminal fragment of Band 3 after carboxypeptidase Y digestion of stripped ghost membranes. No such decrease was observed after carboxypeptidase Y treatment of intact cells. In addition, Band 3 purified from carboxypeptidase Y-treated stripped ghost membranes had a different carboxyl-terminal sequence from intact Band 3. Cleavage of the carboxyl-terminal of Band 3 was also observed when non-stripped ghosts or inside-out vesicles were treated with carboxypeptidase Y. However, the digestion was less extensive. These results suggest that the carboxyl-terminal of Band 3 may be protected from digestion by its association with extrinsic membrane proteins. We conclude, therefore, that the carboxyl-terminal of Band 3 is located on the cytoplasmic side of the red cell membrane. Since the amino-terminal of Band 3 is also located on the cytoplasmic side of the erythrocyte membrane, the Band 3 polypeptide crosses the membrane an even number of times. A model for the folding of Band 3 in the erythrocyte membrane is presented.

Amino Acid Sequence↗