Rotational diffusion of the erythrocyte integral membrane protein band 3: effect of hemichrome binding

Morphometric and Nanomechanical Features of Erythrocytes Characteristic of Early Pregnancy Loss

Early pregnancy loss (EPL) is estimated to be between 15 and 20% of all adverse pregnancies. Approximately, half of EPL cases have no identifiable cause. Herein, we apply atomic force microscopy to evaluate the alteration of morphology and nanomechanics of erythrocytes from women with EPL with unknown etiology, as compared to healthy pregnant (PC) and nonpregnant women (NPC). Freshly isolated erythrocytes from women with EPL differ in both the roughness value (4.6 ± 0.3 nm, p < 0.05), and Young’s modulus (2.54 ± 0.6 MPa, p < 0.01) compared to the values for NPC (3.8 ± 0.4 nm and 0.94 ± 0.2 MPa, respectively) and PC (3.3 ± 0.2 nm and 1.12 ± 0.3 MPa, respectively). Moreover, we find a time-dependent trend for the reduction of the cells’ morphometric parameters (cells size and surface roughness) and the membrane elasticity—much faster for EPL than for the two control groups. The accelerated aging of EPL erythrocytes is expressed in faster morphological shape transformation and earlier occurrence of spiculated and spherical-shaped cells, reduced membrane roughness and elasticity with aging evolution. Oxidative stress in vitro contributed to the morphological cells’ changes observed for EPL senescent erythrocytes. The ultrastructural characteristics of cells derived from women with miscarriages show potential as a supplementary mark for a pathological state.

Cell Physiology and Molecular Mechanism of Anion Transport by Erythrocyte Band 3/AE1

The major transmembrane protein of the red blood cell, known as band 3, AE1, and SLC4A1, has two main functions: 1) catalysis of Cl^-/HCO₃^- exchange, one of the steps in CO₂ excretion; 2) anchoring the membrane skeleton. This review summarizes the 150 year history of research on red cell anion transport and band 3 as an experimental system for studying membrane protein structure and ion transport mechanisms. Important early findings were that red cell Cl^- transport is a tightly coupled 1:1 exchange and band 3 is labeled by stilbenesulfonate derivatives that inhibit anion transport. Biochemical studies showed that the protein is dimeric or tetrameric (paired dimers) and that there is one stilbenedisulfonate binding site per subunit of the dimer. Transport kinetics and inhibitor characteristics supported the idea that the transporter acts by an alternating access mechanism with intrinsic asymmetry. The sequence of band 3 cDNA provided a framework for detailed study of protein topology and amino acid residues important for transport. The identification of genetic variants produced insights into the roles of band 3 in red cell abnormalities and distal renal tubular acidosis. The publication of the membrane domain crystal structure made it possible to propose concrete molecular models of transport. Future research directions include improving our understanding of the transport mechanism at the molecular level and of the integrative relationships among band 3, hemoglobin, carbonic anhydrase, and gradients (both transmembrane and subcellular) of HCO₃^-, Cl^-, O₂, CO₂, pH, and NO metabolites during pulmonary and systemic capillary gas exchange.

Erythrocytes: Central Actors in Multiple Scenes of Atherosclerosis

The development and progression of atherosclerosis (ATH) involves lipid accumulation, oxidative stress and both vascular and blood cell dysfunction. Erythrocytes, the main circulating cells in the body, exert determinant roles in the gas transport between tissues. Erythrocytes have long been considered as simple bystanders in cardiovascular diseases, including ATH. This review highlights recent knowledge concerning the role of erythrocytes being more than just passive gas carriers, as potent contributors to atherosclerotic plaque progression. Erythrocyte physiology and ATH pathology is first described. Then, a specific chapter delineates the numerous links between erythrocytes and atherogenesis. In particular, we discuss the impact of extravasated erythrocytes in plaque iron homeostasis with potential pathological consequences. Hyperglycaemia is recognised as a significant aggravating contributor to the development of ATH. Then, a special focus is made on glycoxidative modifications of erythrocytes and their role in ATH. This chapter includes recent data proposing glycoxidised erythrocytes as putative contributors to enhanced atherothrombosis in diabetic patients.

Alternate and Additional Functions of Erythrocyte Hemoglobin

The review discusses pleiotropic effects of erythrocytic hemoglobin (Hb) and their significance for human health. Hemoglobin is mostly known as an oxygen carrier, but its biochemical functions are not limited to this. The following aspects of Hb functioning are examined: (i) catalytic functions of the heme component (nitrite reductase, NO dioxygenase, monooxygenase, alkylhydroperoxidase) and of the apoprotein (esterase, lipoxygenase); (ii) participation in nitric oxide metabolism; (iii) formation of membrane-bound Hb and its role in the regulation of erythrocyte metabolism; (iv) physiological functions of Hb catabolic products (iron, CO, bilirubin, peptides). Special attention is given to Hb participation in signal transduction in erythrocytes. The relationships between various erythrocyte metabolic parameters, such as oxygen status, ATP formation, pH regulation, redox balance, and state of the cytoskeleton are discussed with regard to Hb. Hb polyfunctionality can be considered as a manifestation of the principle of biochemical economy.

Red Blood Cell Susceptibility to Pneumolysin: CORRELATION WITH MEMBRANE BIOCHEMICAL AND PHYSICAL PROPERTIES

This study investigated the effect of the biochemical and biophysical properties of the plasma membrane as well as membrane morphology on the susceptibility of human red blood cells to the cholesterol-dependent cytolysin pneumolysin, a key virulence factor of Streptococcus pneumoniae, using single cell studies. We show a correlation between the physical properties of the membrane (bending rigidity and surface and dipole electrostatic potentials) and the susceptibility of red blood cells to pneumolysin-induced hemolysis. We demonstrate that biochemical modifications of the membrane induced by oxidative stress, lipid scrambling, and artificial cell aging modulate the cell response to the toxin. We provide evidence that the diversity of response to pneumolysin in diabetic red blood cells correlates with levels of glycated hemoglobin and that the mechanical properties of the red blood cell plasma membrane are altered in diabetes. Finally, we show that diabetic red blood cells are more resistant to pneumolysin and the related toxin perfringolysin O relative to healthy red blood cells. Taken together, these studies indicate that the diversity of cell response to pneumolysin within a population of human red blood cells is influenced by the biophysical and biochemical status of the plasma membrane and the chemical and/or oxidative stress pre-history of the cell.

Effect of hydroperoxides on red blood cell membrane mechanical properties

We investigate the effect of oxidative stress on red blood cell membrane mechanical properties in vitro using detailed analysis of the membrane thermal fluctuation spectrum. Two different oxidants, the cytosol-soluble hydrogen peroxide and the membrane-soluble cumene hydroperoxide, are used, and their effects on the membrane bending elastic modulus, surface tension, strength of confinement due to the membrane skeleton, and 2D shear elastic modulus are measured. We find that both oxidants alter significantly the membrane elastic properties, but their effects differ qualitatively and quantitatively. While hydrogen peroxide mainly affects the elasticity of the membrane protein skeleton (increasing the membrane shear modulus), cumene hydroperoxide has an impact on both membrane skeleton and lipid bilayer mechanical properties, as can be seen from the increased values of the shear and bending elastic moduli. The biologically important implication of these results is that the effects of oxidative stress on the biophysical properties, and hence the physiological functions, of the cell membrane depend on the nature of the oxidative agent. Thermal fluctuation spectroscopy provides a means of characterizing these different effects, potentially in a clinical milieu.

Regulation of membrane-cytoskeletal interactions by tyrosine phosphorylation of erythrocyte band 3

The cytoplasmic domain of band 3 serves as a center of erythrocyte membrane organization and constitutes the major substrate of erythrocyte tyrosine kinases. Tyrosine phosphorylation of band 3 is induced by several physiologic stimuli, including malaria parasite invasion, cell shrinkage, normal cell aging, and oxidant stress (thalassemias, sickle cell disease, glucose-6-phosphate dehydrogenase deficiency, etc). In an effort to characterize the biologic sequelae of band 3 tyrosine phosphorylation, we looked for changes in the polypeptide's function that accompany its phosphorylation. We report that tyrosine phosphorylation promotes dissociation of band 3 from the spectrin-actin skeleton as evidenced by: (1) a decrease in ankyrin affinity in direct binding studies, (2) an increase in detergent extractability of band 3 from ghosts, (3) a rise in band 3 cross-linkability by bis-sulfosuccinimidyl-suberate, (4) significant changes in erythrocyte morphology, and (5) elevation of the rate of band 3 diffusion in intact cells. Because release of band 3 from its ankyrin and adducin linkages to the cytoskeleton can facilitate changes in multiple membrane properties, tyrosine phosphorylation of band 3 is argued to enable adaptive changes in erythrocyte biology that permit the cell to respond to the above stresses.

Selective permeabilization of the host cell membrane of Plasmodium falciparum-infected red blood cells with streptolysin O and equinatoxin II

Plasmodium falciparum develops within the mature RBCs (red blood cells) of its human host in a PV (parasitophorous vacuole) that separates the host cell cytoplasm from the parasite surface. The pore-forming toxin, SLO (streptolysin O), binds to cholesterol-containing membranes and can be used to selectively permeabilize the host cell membrane while leaving the PV membrane intact. We found that in mixtures of infected and uninfected RBCs, SLO preferentially lyses uninfected RBCs rather than infected RBCs, presumably because of differences in cholesterol content of the limiting membrane. This provides a means of generating pure preparations of viable ring stage infected RBCs. As an alternative permeabilizing agent we have characterized EqtII (equinatoxin II), a eukaryotic pore-forming toxin that binds preferentially to sphingomyelin-containing membranes. EqtII lyses the limiting membrane of infected and uninfected RBCs with similar efficiency but does not disrupt the PV membrane. It generates pores of up to 100 nm, which allow entry of antibodies for immunofluorescence and immunogold labelling. The present study provides novel tools for the analysis of this important human pathogen and highlights differences between Plasmodium-infected and uninfected RBCs.

Plasmodium falciparum induces reorganization of host membrane proteins during intraerythrocytic growth

The virulence of the malaria parasite, Plasmodium falciparum, is due in large part to the way in which it modifies the membrane of its erythrocyte host. In this work we have used confocal microscopy and fluorescence recovery after photo-bleaching to examine the lateral mobility of host membrane proteins in erythrocytes infected with P falciparum at different stages of parasite growth. The erythrocyte membrane proteins band 3 and glycophorin show a marked decrease in mobility during the trophozoite stage of growth. Erythrocytes infected with a parasite strain that does not express the knob-associated histidine-rich protein show similar effects, indicating that this parasite protein does not contribute to the immobilization of the host proteins. Erythrocytes infected with ring-stage parasites exhibit intermediate mobility indicating that the parasite is able to modify its host prior to its active feeding stage.

A general NMR method for rapid, efficient, and reliable biochemical screening

High-throughput screening is usually the method of drug-lead discovery. It is now well accepted that, for a functional assay, quality is more important than quantity. The ligand-based or protein-based NMR screening methodologies for detecting compounds binding to the macromolecular target of interest are now well established. A novel and sensitive NMR method for rapid, efficient, and reliable biochemical screening is presented. The method named 3-FABS (three fluorine atoms for biochemical screening) requires the labeling of the substrate with a CF(3) moiety and utilizes (19)F NMR spectroscopy for the detection of the starting and enzymatically modified substrates. The method allows for high-quality screening of large compound or natural product extract collections and for measuring their IC(50) values. Applications of this technique to the screening of inhibitors of the Ser/Thr kinase AKT1 and the protease trypsin are presented. In addition, an interesting application of 3-FABS to functional genomics is also presented.

Flexibility of the cytoplasmic domain of the anion exchange protein, band 3, in human erythrocytes

The rotational flexibility of the cytoplasmic domain of band 3, in the region that is proximal to the inner membrane surface, has been investigated using a combination of time-resolved optical anisotropy (TOA) and saturation-transfer electron paramagnetic resonance (ST-EPR) spectroscopies. TOA studies of rotational diffusion of the transmembrane domain of band 3 show a dramatic decrease in residual anisotropy following cleavage of the link with the cytoplasmic domain by trypsin (E. A. Nigg and R. J. Cherry, 1980, Proc. Natl. Acad. Sci. U.S.A. 77:4702-4706). This result is compatible with two independent hypotheses: 1) trypsin cleavage leads to dissociation of large clusters of band 3 that are immobile on the millisecond time scale, or 2) trypsin cleavage leads to release of a constraint to uniaxial rotational diffusion of the transmembrane domain. ST-EPR studies at X- and Q-band microwave frequencies detect rotational diffusion of the transmembrane domain of band 3 about the membrane normal axis of reasonably large amplitude that does not change upon cleavage with trypsin. These ST-EPR results are not consistent with dissociation of clusters of band 3 as a result of cleavage with trypsin. Global analyses of the ST-EPR data using a newly developed algorithm indicate that any constraint to rotational diffusion of the transmembrane domain of band 3 via interactions of the cytoplasmic domain with the membrane skeleton must be sufficiently weak to allow rotational excursions in excess of 32 degrees full-width for a square-well potential. In support of this result, analyses of the TOA data in terms of restricted amplitude uniaxial rotational diffusion models suggest that the membrane-spanning domain of that population of band 3 that is linked to the membrane skeleton is constrained to diffuse in a square-well of approximately 73 degrees full-width. This degree of flexibility may be necessary for providing the unique mechanical properties of the erythrocyte membrane.

Regulation of the glycophorin C-protein 4.1 membrane-to-skeleton bridge and evaluation of its contribution to erythrocyte membrane stability

The band 3-ankyrin-spectrin bridge and the glycophorin C-protein 4.1-spectrin/actin bridge constitute the two major tethers between the erythrocyte membrane and its spectrin skeleton. Although a structural requirement for the band 3-ankyrin bridge is well established, the contribution of the glycophorin C-protein 4.1 bridge to red cell function remains to be defined. In order to explore this latter bridge further, we have identified and/or characterized five stimuli that sever the linkage in intact erythrocytes and have examined the impact of this rupture on membrane mechanical properties. We report here that elevation of cytosolic 2,3-bisphosphoglycerate, an increase in intracellular Ca(2+), removal of cell O(2), a decrease in intracellular pH, and activation of erythrocyte protein kinase C all promote dissociation of protein 4.1 from glycophorin C, leading to reduced retention of glycophorin C in detergent-extracted spectrin/actin skeletons. Significantly, where mechanical studies could be performed, we also observe that rupture of the membrane-to-skeleton bridge has little or no impact on the mechanical properties of the cell, as assayed by ektacytometry and nickel mesh filtration. We, therefore, suggest that, although regulation of the glycophorin C-protein 4.1-spectrin/actin bridge likely occurs physiologically, the role of the tether and the associated regulatory changes remain to be established.

Targeted Inactivation of Murine Band 3 (AE1) Gene Produces a Hypercoagulable State Causing Widespread Thrombosis In Vivo

Only 5% to 10% of band 3 null mice survive the neonatal period. To determine the cause of death, 3 adult and 11 newborn band 3 null mice were submitted for histopathologic examination. All but 1 pup showed evidence of thrombosis including: (1) large thrombotic lesions in the heart, which were partially organized, calcified in some fields, and endothelialized, indicating a process that developed premortem (3 of 3 adults and 6 of 11 pups). (2) Subcapsular necrotic areas in the liver suggestive of premortem ischemic events caused by arteriolar occlusions (8 of 11 pups). (3) Large vein thrombi (4 of 11 pups). To investigate the etiology of this hypercoagulable state, we have used the Russell’s viper venom test (RVV) to show that red blood cells (RBCs) from band 3 null mice significantly shorten the RVV clotting time of normal plasma in a dose-dependent fashion, whereas RBCs from normal mice have no effect, suggesting that the membrane of band 3 null RBCs provides a suitable surface for activation of the prothrombinase complex. Using flow cytometry, we have examined the phosphatidylserine (PS)-specific binding of fluorescein isothiocyanate (FITC)-annexin V to normal and band 3 null RBCs. A subpopulation of cells (3% to 5% of RBCs) with increased FITC-annexin V binding was detected in band 3 null RBCs as compared with normal RBCs. Furthermore, the entire cell population of band 3 null RBCs shows a measurable increase in the mean fluorescence intensity, suggesting that band 3 null RBCs may have increased PS exposure on the outer membrane leaflet. These findings are further supported by direct fluorescence microscopy of normal and band 3 null RBCs labeled with FITC-annexin V. Based on these observations, we postulate that the high mortality of band 3 null mice may be related to a hypercoagulable state, which appears to originate from changes in the phospholipid composition of the membrane leading to PS exposure on the outer leaflet.

© 1998 by The American Society of Hematology.

Targeted Inactivation of Murine Band 3 (AE1) Gene Produces a Hypercoagulable State Causing Widespread Thrombosis In Vivo

Only 5% to 10% of band 3 null mice survive the neonatal period. To determine the cause of death, 3 adult and 11 newborn band 3 null mice were submitted for histopathologic examination. All but 1 pup showed evidence of thrombosis including: (1) large thrombotic lesions in the heart, which were partially organized, calcified in some fields, and endothelialized, indicating a process that developed premortem (3 of 3 adults and 6 of 11 pups). (2) Subcapsular necrotic areas in the liver suggestive of premortem ischemic events caused by arteriolar occlusions (8 of 11 pups). (3) Large vein thrombi (4 of 11 pups). To investigate the etiology of this hypercoagulable state, we have used the Russell’s viper venom test (RVV) to show that red blood cells (RBCs) from band 3 null mice significantly shorten the RVV clotting time of normal plasma in a dose-dependent fashion, whereas RBCs from normal mice have no effect, suggesting that the membrane of band 3 null RBCs provides a suitable surface for activation of the prothrombinase complex. Using flow cytometry, we have examined the phosphatidylserine (PS)-specific binding of fluorescein isothiocyanate (FITC)-annexin V to normal and band 3 null RBCs. A subpopulation of cells (3% to 5% of RBCs) with increased FITC-annexin V binding was detected in band 3 null RBCs as compared with normal RBCs. Furthermore, the entire cell population of band 3 null RBCs shows a measurable increase in the mean fluorescence intensity, suggesting that band 3 null RBCs may have increased PS exposure on the outer membrane leaflet. These findings are further supported by direct fluorescence microscopy of normal and band 3 null RBCs labeled with FITC-annexin V. Based on these observations, we postulate that the high mortality of band 3 null mice may be related to a hypercoagulable state, which appears to originate from changes in the phospholipid composition of the membrane leading to PS exposure on the outer leaflet.

© 1998 by The American Society of Hematology.

Oligomeric state of human erythrocyte band 3 measured by fluorescence resonance energy homotransfer

The oligomeric state of the erythrocyte anion exchange protein, band 3, has been assayed by resonance energy homotransfer. Homotransfer between oligomeric subunits, labeled with eosin-5-maleimide at Lys430 in the transmembrane domain, has been demonstrated by steady-state and time-resolved fluorescence spectroscopy, and is readily observed by its depolarization of the eosin fluorescence. Polarized fluorescence measurements of HPLC-purified band 3 oligomers indicate that eosin homotransfer increases progressively with increasing species size. This shows that homotransfer also occurs between labeled band 3 dimers as well as within the dimers, making fluorescence anisotropy measurements sensitive to band 3 self-association. Treatment of ghost membranes with either Zn2+ or melittin, agents that cluster band 3, significantly decreases the anisotropy as a result of the increased homotransfer within the band 3 clusters. By comparison with the anisotropy of species of known oligomeric state, the anisotropy of erythrocyte ghost membranes at 37 degrees C is consistent with dimeric and/or tetrameric band 3, and does not require postulation of a fraction of large clusters. Proteolytic removal of the cytoplasmic domain of band 3, which significantly increases the rotational mobility of the transmembrane domain, does not affect its oligomeric state, as reported by eosin homotransfer. These results support a model in which interaction with the membrane skeleton restricts the mobility of band 3 without significantly altering its self-association state.

Complete Deficiency of Glycophorin A in Red Blood Cells From Mice With Targeted Inactivation of the Band 3 (AE1) Gene

Glycophorin A is the major transmembrane sialoglycoprotein of red blood cells. It has been shown to contribute to the expression of the MN and Wright blood group antigens, to act as a receptor for the malaria parasite Plasmodium falciparum and Sendai virus, and along with the anion transporter, band 3, may contribute to the mechanical properties of the red blood cell membrane. Several lines of evidence suggest a close interaction between glycophorin A and band 3 during their biosynthesis. Recently, we have generated mice where the band 3 expression was completely eliminated by selective inactivation of the AE1 anion exchanger gene, thus allowing us to study the effect of band 3 on the expression of red blood cell membrane proteins. In this report, we show that the band 3 −/− red blood cells contain protein 4.1, adducin, dematin, p55, and glycophorin C. In contrast, the band 3 −/− red blood cells are completely devoid of glycophorin A (GPA), as assessed by Western blot and immunocytochemistry techniques, whereas the polymerase chain reaction (PCR) confirmed the presence of GPA mRNA. Pulse-label and pulse-chase experiments show that GPA is not incorporated in the membrane and is rapidly degraded in the cytoplasm. Based on these findings and other published evidence, we propose that band 3 plays a chaperone-like role, which is necessary for the recruitment of GPA to the red blood cell plasma membrane.

Spectroscopic and kinetic characterization of eosin-5-maleimide

Eosin-5-maleimide (EM) is an increasingly important and widely used probe in the study of membrane protein structure and function. Yet little is known about its spectral properties in hydrophobic and hydrophilic environments. Furthermore, EM is hydrolyzed faster than the traditional N-ethylmaleimide. To offer a more solid foundation for the use of EM in studies of membrane protein structure and function, we have undertaken a detailed study of the absorbance and fluorescence spectra of EM, eosin-5-maleic acid, and the L-cysteine and beta-mercaptoethanol adducts of EM in aqueous and hydrophobic environments; we have studied the kinetics of hydrolysis of EM in various environments, and we have investigated the reaction kinetics of EM with L-cysteine.

Complete Deficiency of Glycophorin A in Red Blood Cells From Mice With Targeted Inactivation of the Band 3 (AE1) Gene

Glycophorin A is the major transmembrane sialoglycoprotein of red blood cells. It has been shown to contribute to the expression of the MN and Wright blood group antigens, to act as a receptor for the malaria parasite Plasmodium falciparum and Sendai virus, and along with the anion transporter, band 3, may contribute to the mechanical properties of the red blood cell membrane. Several lines of evidence suggest a close interaction between glycophorin A and band 3 during their biosynthesis. Recently, we have generated mice where the band 3 expression was completely eliminated by selective inactivation of the AE1 anion exchanger gene, thus allowing us to study the effect of band 3 on the expression of red blood cell membrane proteins. In this report, we show that the band 3 −/− red blood cells contain protein 4.1, adducin, dematin, p55, and glycophorin C. In contrast, the band 3 −/− red blood cells are completely devoid of glycophorin A (GPA), as assessed by Western blot and immunocytochemistry techniques, whereas the polymerase chain reaction (PCR) confirmed the presence of GPA mRNA. Pulse-label and pulse-chase experiments show that GPA is not incorporated in the membrane and is rapidly degraded in the cytoplasm. Based on these findings and other published evidence, we propose that band 3 plays a chaperone-like role, which is necessary for the recruitment of GPA to the red blood cell plasma membrane.

Hereditary spherocytosis: a review of the clinical and molecular aspects of the disease

Hereditary spherocytosis is a common and very heterogeneous hemolytic anemia caused by defects of the red cell membrane proteins. In recent years, major advances in our understanding of the red cell membrane skeleton and a better characterization of its individual components have allowed a brighter insight into the pathogenesis of the disease. In this article, we present an overview of the erythrocyte skeleton and its individual constituents. We also review the clinical aspects of the disease and describe the currently known molecular defects involving the membrane proteins which have been shown to play an essential role in the underlying mechanism of hereditary spherocytosis. Finally we examine several models that have been proposed in an attempt to clarify the mechanism leading from the initial molecular insult to the clinical phenotype.

The orientation of eosin-5-maleimide on human erythrocyte band 3 measured by fluorescence polarization microscopy

The dominant motional mode for membrane proteins is uniaxial rotational diffusion about the membrane normal axis, and investigations of their rotational dynamics can yield insight into both the oligomeric state of the protein and its interactions with other proteins such as the cytoskeleton. However, results from the spectroscopic methods used to study these dynamics are dependent on the orientation of the probe relative to the axis of motion. We have employed polarized fluorescence confocal microscopy to measure the orientation of eosin-5-maleimide covalently reacted with Lys-430 of human erythrocyte band 3. Steady-state polarized fluorescence images showed distinct intensity patterns, which were fit to an orientation distribution of the eosin absorption and emission dipoles relative to the membrane normal axis. This orientation was found to be unchanged by trypsin treatment, which cleaves band 3 between the integral membrane domain and the cytoskeleton-attached domain. this result suggests that phosphorescence anisotropy changes observed after trypsin treatment are due to a rotational constraint change rather than a reorientation of eosin. By coupling time-resolved prompt fluorescence anisotropy with confocal microscopy, we calculated the expected amplitudes of the e-Dt and e-4Dt terms from the uniaxial rotational diffusion model and found that the e-4Dt term should dominate the anisotropy decay. Delayed fluorescence and phosphorescence anisotropy decays of control and trypsin-treated band 3 in ghosts, analyzed as multiple uniaxially rotating populations using the amplitudes predicted by confocal microscopy, were consistent with three motional species with uniaxial correlation times ranging from 7 microseconds to 1.4 ms.

A tethered adhesive particle model of two-dimensional elasticity and its application to the erythrocyte membrane

A new model of two-dimensional elasticity with application to the erythrocyte membrane is proposed. The system consists of a planar array of self-adhesive particles attached to nearest neighbors with flexible tethers. Stretching from the equilibrium dimension is resisted because force is required to dissociate the particle clusters and to decrease the distribution entropy. Release of the external force is accompanied by a contraction as thermal diffusion randomizes the particles and allows interparticle attachments to form again. Analysis of membrane thermodynamics and mechanics under the two-state particle assumption results in a shear softening stress-strain relation. The shear modulus is found proportional to the square root of the surface density of particles, the interparticle adhesive energy, and is inversely proportional to the tether length. Applied to the erythrocyte membrane under the assumption that band 3 tetramer represents the particle and spectrin the tether, the shear modulus predicted corresponds to the measured value when the interparticle adhesive energy is approximately 4.0-5.9 kT, where kT is the Boltzmann constant multiplied by the temperature. This model suggests a mechanism wherein erythrocyte membrane deformability depends on integral protein homomultimeric interactions and can be modulated from the external surface.

In vitro effects of oestradiol and indomethacin on rabbit erythrocyte fragility characteristics

An in vitro study was conducted to determine whether indomethacin (IN) and oestradiol (E(2)) induced decreases in rabbit haematocrit may be related to their effect on erythrocyte fragility (EF). Aliquots of treated rabbit whole blood were assayed as control, IN (9.6 mug/ml), E(2) (500 pg/ml) and IN + E(2), for changes in EF. Osmotic (OF) and mechanical (MF) fragility in eight experimental replicates were evaluated under approximate physiological conditions by measurement of haemoglobin release. Samples were assayed immediately after drug addition and again 4 hr after incubation at 39.5 degrees C. OF results showed a significant increase in 50% haemolysis between final IN and IN + E(2) values when compared with their initial values and with controls. OF haemolysis dispersion was increased over time by IN and IN + E(2). MF increased with IN, E(2) and IN + E(2) versus their initial values and the controls. Although the increase in MF from IN was greater than that from E(2), the MF from IN + E(2) was not greater than that from IN alone. The IN induced increases in both OF and MF indicate a difference in degree of interaction with the erythrocyte from that of E(2), which affected only MF and the effect of which was neither additive nor synergistic with that of IN.

Analysis of saturation transfer electron paramagnetic resonance spectra of a spin-labeled integral membrane protein, band 3, in terms of the uniaxial rotational diffusion model

Algorithms have been developed for the calculation of saturation transfer electron paramagnetic resonance (ST-EPR) spectra of a nitroxide spin-label assuming uniaxial rotational diffusion, a model that is frequently used to describe the global rotational dynamics of large integral membrane proteins. One algorithm explicitly includes terms describing Zeeman overmodulation effects, whereas the second more rapid algorithm treats these effects approximately using modified electron spin-lattice and spin-spin relaxation times. Simulations are presented to demonstrate the sensitivity of X-band ST-EPR spectra to the rate of uniaxial rotational diffusion and the orientation of the nitroxide probe with respect to the diffusion axis. Results obtained by using the algorithms presented, which are based on the transition-rate formalism, are in close agreement with those obtained by using an eigenfunction expansion approach. The effects of various approximations used in the simulation algorithms are considered in detail. Optimizing the transition-rate formalism to model uniaxial rotational diffusion results in over an order of magnitude reduction in computation time while allowing treatment of nonaxial A- and g-tensors. The algorithms presented here are used to perform nonlinear least-squares analyses of ST-EPR spectra of the anion exchange protein of the human erythrocyte membrane, band 3, which has been affinity spin-labeled with a recently developed dihydrostilbene disulfonate derivative, [15N,2H13]-SL-H2DADS-MAL. These results suggest that all copies of band 3 present in intact erythrocytes undergo rotational diffusion about the membrane normal axis at a rate consistent with a band 3 dimer.

The multiple functions of hemoglobin

The aim of this review is to focus and discuss several parallel biological functions of hemoglobin besides its basic function of oxygen transport. In light of the information present in the literature the following possible physiological roles of hemoglobin are discussed: (1) hemoglobin as molecular heat transducer through its oxygenation-deoxygenation cycle, (2) hemoglobin as modulator of erythrocyte metabolism, (3) hemoglobin oxidation as an onset of erythrocyte senescence, (4) hemoglobin and its implication in genetic resistance to malaria, (5) enzymatic activities of hemoglobin and interactions with drugs, and (6) hemoglobin as source of physiological active catabolites.

Band 3 protein: structure, flexibility and function

The electroneutral exchange of chloride and bicarbonate across the human erythrocyte membrane is facilitated by Band 3, a 911 amino acid glycoprotein. The 43 kDa amino-terminal cytosolic domain binds the cytoskeleton, haemoglobin and glycolytic enzymes. The 52 kDa carboxyl-terminal membrane domain mediates anion transport. The protein is a functional dimer, in which the two subunits probably interact with one another by an allosteric mechanism. It is proposed that the link between the mobile cytoplasmic and the membrane-spanning domains of the protein is flexible, based on recent biochemical, biophysical and structural data. This explains the long-standing puzzle that attachment to the cytoskeletal spectrin and actin does not appear to restrict the rotational movement of the Band 3 protein in the erythrocyte membrane. In the Band 3 isoform from the Southeast Asian Ovalocytes (SAO) this link is altered, resulting a tighter attachment of the cytoskeleton to the plasma membrane and a more rigid red blood cell.

Segmental dynamics of the cytoplasmic domain of erythrocyte band 3 determined by time-resolved fluorescence anisotropy: sensitivity to pH and ligand binding

Interactions between the erythrocyte membrane and its skeleton are mediated primarily by binding of cytoskeletal components to a conformationally sensitive structure, the cytoplasmic domain of band 3 (cdb3). To examine the nanosecond segmental motions of cdb3, band 3 was labeled selectively by fluorescein maleimide at Cys-201 near the proposed hinge in cdb3 about which pH-dependent conformational changes occur. Time-resolved anisotropy of labeled cdb3 in isolated form and in stripped erythrocyte membranes was measured by parallel-acquisition frequency-domain microfluorimetry. Samples had a single-component fluorescein lifetime of approximately 4 ns. Multifrequency phase and modulation data (5-200 MHz) fitted well to a segmental motion model containing two correlation times (tau 1c and tau 2c) and two limiting anisotropies (r1infinity and r2infinity). Measurements in protease-cleaved and denatured samples indicated that tau 1c (100-150 ps) corresponded to rapid rotation of bound fluorescein and tau 2c (2-5 ns) corresponded to segmental motion of cdb3. Both motions were hindered as quantified by nonzero r1infinity and r2infinity. The strong pH dependence of segmental motion correlated with that of cdb3 conformation measured by intrinsic tryptophan fluorescence. Significant changes in cdb3 segmental motion occurred upon interactions with the small ligands 2,3-bisphosphoglycerate and calcium and several glycolytic enzymes known to bind to the N terminus of band 3. These time-resolved fluorescence measurements of the nanosecond segmental dynamics of a labeled membrane protein provide evidence for the sensitivity of cdb3 conformation to ligand binding and suggest long-range structural communication through cdb3.

Proteolytic digestion of band 3 at an external site alters the erythrocyte membrane organisation and may facilitate malarial invasion

Invasion of human erythrocytes by Plasmodium falciparum is inhibited by chymostatin. This suggests that digestion of erythrocyte surface proteins by a protease with chymotrypsin-like activity may be involved in the invasion process. We find that treatment of intact erythrocytes with chymotrypsin cleaves the integral membrane protein, band 3, generating a major fragment with an apparent molecular weight of 58 kDa. We have used measurements of the rotational mobility of band 3, labelled with the phosphorescence probe, eosin-5-maleimide, as a monitor of the changes in the molecular organisation of the erythrocyte membrane which accompany band 3 cleavage. We report that the chymotrypsin treatment increases the rotational freedom of band 3, possibly due to conformational changes which disrupt its interaction with the underlying peripheral membrane proteins. We also show that chymotrypsin-treated erythrocytes undergo extensive endocytosis upon incorporation of exogenous fluorescently labelled phospholipid. We suggest that during the invasion process, digestion of band 3 by a chymotrypsin-like protease may induce a localised disruption of the erythrocyte membrane. This destabilised region of membrane may represent the site for the insertion of parasite-derived phospholipid, thus allowing the formation of the parasitophorous vacuole membrane.

Band 3 mobility in camelid elliptocytes: implications for erythrocyte shape

Measurements of time-resolved phosphorescence anisotropy were used to monitor the rotational diffusion of eosin-labeled band 3 in membranes of the elliptocytic erythrocytes of alpacas and camels. The rotational freedom of camelid band 3 was more restricted than for human band 3. Removal of the peripheral membrane proteins from human erythrocyte membranes, by high-pH treatment, increased the band 3 rotational freedom. The same high-pH treatment of alpaca and camel erythrocyte membranes failed to alter the rotational freedom of band 3 in these species and also failed to remove ankyrin. Treatment of human and alpaca erythrocyte membranes with trypsin, which removed the cytoplasmic domain of band 3, caused a marked increase in band 3 rotational freedom in both species. We suggest that ankyrin may modulate the rotational freedom of band 3 in camelid erythrocytes, thereby influences the erythrocyte shape and deformability. The rotational freedom of band 3 in sheep, pig, and rat erythrocyte membranes was also examined and found to be slightly greater than for human band 3. This is consistent with the inability of glyceraldehyde-3-phosphate dehydrogenase to bind to band 3 in the erythrocyte membranes of these species.

Structural organisation of band 3 in Melanesian ovalocytes

The diffusional freedom of human erythrocyte band 3 (anion exchanger 1) has been measured in membranes from normocytic and ovalocytic erythrocytes. A dramatic reorganisation of band 3 in the ovalocyte membranes is indicated by a markedly restricted rotational mobility. Extraction of spectrin from erythrocyte membranes had no effect on normocyte band 3 mobility, but partially relieved the restrictions on ovalocyte band 3 mobility. Further removal of ankyrin and band 4.2 resulted in an increase in the rotational mobility of both ovalocyte and normocyte band 3 to similar levels. The results suggest that the molecular basis of the unusual shape and decreased deformability of ovalocytes resides in an altered interaction of band 3 with one or more of the peripheral proteins. We present a model which illustrates a possible role for band 3 aggregation in controlling erythrocyte deformability.