Increase of the negative charge of erythrocyte membrane proteins in hereditary neuromuscular diseases

The parameters of erythrocyte ghost protein's fluorophores by nitrate's anions were studied in patients with various hereditary myodystrophy. In all the groups under examination the share of fluorophores accessible to a quencher was close to 1. In erythrocyte membranes of healthy donors the relevant constant quenchering was about 17.3 +/- 1.9 M-1 while those of patients were decreased by 3.1 (Duchenne's myodystrophy) and by about 2.0 (other forms of primary and secondary progressive muscular dystrophies). The most probable reason for the decreasing constant of quenchering is the increase of negative charges on the erythrocyte membrane proteins.     

Lateral mobility of negative charge sites at the surface of sheep erythrocytes

Neuraminidase-sensitive negative charge sites on sheep red blood cells (SRBCs) are uniformly distributed over the cell surface, as in other species. Unlike most other species in which charge sites are immobile, however, in intact RBCs interaction of SRBCs with cationized ferritin (CF) induces clustering (i.e. patching) of CF-binding sites. This clustering is both time- and temperature-dependent. The clustering of negative charge sites results in the formation of domains up to 1 000 Å across which are totally free of CF binding sites. The unusually high degree of lateral mobility of ionogenic groups at the SRBC surface may contribute to the species specificity of E rosetting.     

The surface charge of human glutaraldehyde-fixed erythrocytes

We measured the number of charged residues at the surface of fresh human erythrocytes after fixation with glutaraldehyde by polyelectrolyte titration using polycations of different chemical composition and various molecular weights. Independent of the reagents used, the number was (8.5 +/- 1.5) X 10(8) negatively charged residues per cell. The surface charge density of 6.3 e/nm2 is considerably higher than that calculated from the electrophoretic mobility for which the surface charge density is calculated to be 0.09 e/nm2.     

Vesicle-mediated trafficking of parasite proteins to the host cell cytosol and erythrocyte surface membrane in Plasmodium falciparum infected erythrocytes

During the development of the asexual stage of the malaria parasite, Plasmodium falciparum, the composition, structure and function of the host cell membrane is dramatically altered, including the ability to adhere to vascular endothelium. Crucial to these changes is the transport of parasite proteins, which become associated with or inserted into the erythrocyte membrane. Protein and membrane targeting beyond the parasite plasma membrane must require unique pathways, given the parasites intracellular location within a parasitophorous vacuolar membrane and the lack of organelles and biosynthetic machinery in the host cell necessary to support a secretory system. It is not clear how these proteins cross the parasitophorous vacuolar membrane or how they traverse the erythrocyte cytosol to reach their final destinations. The identification of: (1) a P. falciparum homologue of the protein Sar1p, which is an essential component of the COPII-based secretory system in mammalian cells and yeast and (2) electron-dense, possibly coated, secretory vesicles bearing P. falciparum erythrocyte membrane protein 1 and P. falciparum erythrocyte membrane protein 3 in the host cell cytosol of P. falciparum infected erythrocytes recently provided the first direct evidence of a vesicle-mediated pathway for the trafficking of some parasite proteins to the erythrocyte membrane. The major advance in uncovering the parasite-induced secretory pathway was made by incubating infected erythrocytes with aluminium tetrafluoride, an activator of guanidine triphosphate-binding proteins, which resulted in the accumulation of the vesicles into multiple vesicle strings. These vesicle complexes were often associated with and closely abutted the erythrocyte membrane, but were apparently prevented from fusing by the aluminium fluoride treatment, making their capture by electron microscopy possible. It appears that malaria parasites export proteins into the host cell cytosol to support a vesicle-mediated protein trafficking pathway.     

Ultrastructural localization of erythrocyte cytoskeletal and integral membrane proteins in Plasmodium falciparum-infected erythrocytes

The distributions of ankyrin, spectrin, band 3, and glycophorin A were examined in Plasmodium falciparum-infected erythrocytes by immunoelectron microscopy to determine whether movement of parasite proteins and membrane vesicles between the parasitophorous vacuole membrane and erythrocyte surface membrane involves internalization of host membrane skeleton proteins. Monospecific rabbit antisera to spectrin, band 3 and ankyrin and a mouse monoclonal antibody to glycophorin A reacted with these erythrocyte proteins in infected and uninfected human erythrocytes by immunoblotting. Cross-reacting malarial proteins were not detected. The rabbit sera also failed to immunoprecipitate [3H]isoleucine labeled malarial proteins from Triton X-100 and sodium dodecyl sulfate (SDS) extracts of infected erythrocytes. These three antibodies as well as the monoclonal antibody to glycophorin A bound to the membrane skeleton of infected and uninfected erythrocytes. The parasitophorous vacuole membrane was devoid of bound antibody, a result indicating that this membrane contains little, if any, of these host membrane proteins. With ring-, trophozoite- and schizont-infected erythrocytes, spectrin, band 3 and glycophorin A were absent from intracellular membranes including Maurer's clefts and other vesicles in the erythrocyte cytoplasm. In contrast, Maurer's clefts were specifically labeled by anti-ankyrin antibody. There was a slight, corresponding decrease in labeling of the membrane skeleton of infected erythrocytes. A second, morphologically distinct population of circular, vesicle-like membranes in the erythrocyte cytoplasm was not labeled with anti-ankyrin antibody. We conclude that membrane movement between the host erythrocyte surface membrane and parasitophorous vacuole membrane involves preferential sorting of ankyrin into a subpopulation of cytoplasmic membranes.     

Roles of surface electrochemistry and macromolecular adsorption in heparin-induced red blood cell aggregation

Red blood cell (RBC) aggregation in heparin-saline solution was quantified by microscopic observation. The adsorption isotherms of heparin onto normal and neuraminidase-treated RBC surfaces were determined by radioactive heparin labeled with 125I-Bolton-Hunter Reagent. RBC aggregation by heparin requires the presence of sialic acids at cell surface and was enhanced by reduction of ionic strength of the suspending medium. Adsorption of heparin onto RBC surface was increased by removal of sialic acids. These findings not only serve to elucidate the basic mechanism of cell-cell interaction mediated by negatively charged macromolecules, but also provide experimental evidence for the possible conformational change of macromolecules at the charged surface.     

Characterization of calpain I-binding proteins in human erythrocyte plasma membrane

The calpain-binding components on the plasma membrane were characterized using calpain I. 125I-labeled calpain was bound to inside-out membrane vesicles from human erythrocyte in a Ca2(+)-dependent manner, but not to right-side-out membrane vesicles. The maximum binding was observed at more than 5 microM Ca2+. The binding amount of calpain to the inside-out membrane vesicles was decreased when the vesicles were pretreated with 100 micrograms/ml of trypsin, chymotrypsin, elastase, or pronase P for 30 min at 37 degrees C, although the binding to the vesicles pretreated with 200 micrograms/ml of phospholipase A2 or C was not affected. Calpain-binding proteins in the membrane were analyzed by using a modified immunoblotting for calpain. Immunostained bands of 240, 220, 89, 72, 52, and 36 kDa were detected as the calpain-binding proteins in the native membrane. All of these bands had disappeared in trypsin-treated membrane. The disappearance of bands was dose-dependent with respect to trypsin and paralleled the reduction of binding amount of calpain to the trypsinized membrane. In calpain-treated membrane, the 240 and 36 kDa bands were retained in the blotting, though the other bands disappeared dose-dependently with respect to calpain. These results suggested that the significant component in the inner surface of plasma membrane for binding of calpain was proteinaceous and the calpain-binding proteins could be classified into two species, i.e. substrates of calpain (220, 89, 72, and 52 kDa protein) and non-substrates (240 and 36 kDa protein).     

Relative influence of hydrophobicity and net charge in the aggregation of two homologous proteins

A potentially amyloidogenic protein has to be at least partially unfolded to form amyloid aggregates. However, aggregation of the partially or totally unfolded state of a protein is modulated by at least three other factors: hydrophobicity, propensity to form secondary structure, and net charge of the polypeptide chain. We propose to evaluate the relative importance of net charge, as opposed to the other factors, on protein aggregation and amyloidogenicity. For this aim, we have used two homologous proteins that were previously shown to be able to form amyloid fibrils in vitro, the N-terminal domain of HypF from Escherichia coli (HypF-N) and human muscle acylphosphatase (AcP). The aggregation process from an ensemble of partially unfolded conformations is ca. 1000-fold faster for HypF-N than for AcP. This difference can mainly be attributed to a higher hydrophobicity and a lower net charge for HypF-N than for AcP. By using protein engineering methods, we have decreased the net charge of AcP to a value identical to that of wild-type HypF-N and increased the net charge of HypF-N to a value identical to that of wild-type AcP. Amino acid substitutions were selected to minimize changes in hydrophobicity and secondary structure propensities. We were able to estimate that the difference in net charge between the two wild-type proteins contributes to 20-25% of the difference in their aggregation rates. An understanding of the relative influences of these forces in protein aggregation has implications for elucidating the complexity of the aggregation process, for predicting the effect of natural mutations, and for accurate protein design.     

Effect of oral contraceptives and pregnancy on erythrocyte deformability and surface charge.

Erythrocyte deformability and surface charge were studied in normal premenopausal women, oral contraceptive users, and pregnant women. The increased incidence of thrombosis in women taking oral contraceptives could not be explained by decreased erythrocyte deformability or surface charge. However, the decreased erythrocyte deformability of late pregnancy may relate to thrombosis during this period and to increased hemolysis in patients with certain hemoglobinopathies.     

Determination of erythrocyte aggregation

One of the most common health criteria--erythrocyte sedimentation rate (ESR)--is considered in the paper. It is shown that the simple model presented, based on the generalized Stokes formula, the blood volume conservation law, and the Smoluchowski theory of particles coagulation, makes it possible, on the basis of experimentally recorded sedimentation curves, to identify quantitatively the values of the essential physical parameters of the coupled processes of erythrocyte aggregation and sedimentation. The analytical solution of Smoluchowski equation is used to evaluate the sedimentation and aggregation rate constants. The problem of determining the erythrocyte aggregation rate (EAR) is transformed to a minimization task in which only the experimental results for ESR are needed. Experimentally ESR is measured accurately enough by using an equipment set up just for the purpose. This method of identification could be used as a diagnostic test in hematological laboratories.     

Proteomic profiling of nonenzymatically glycated proteins in human plasma and erythrocyte membranes

Nonenzymatic glycation of peptides and proteins by d-glucose has important implications in the pathogenesis of diabetes mellitus, particularly in the development of diabetic complications. In this work, we report the first proteomics-based characterization of nonenzymatically glycated proteins in human plasma and erythrocyte membranes from individuals with normal glucose tolerance, impaired glucose tolerance, and type 2 diabetes mellitus. Phenylboronate affinity chromatography was used to enrich glycated proteins and glycated tryptic peptides from both human plasma and erythrocyte membranes. The enriched peptides were subsequently analyzed by liquid chromatography coupled with electron transfer dissociation-tandem mass spectrometry, resulting in the confident identification of 76 and 31 proteins from human plasma and erythrocyte membranes, respectively. Although most of the glycated proteins could be identified in samples from individuals with normal glucose tolerance, slightly higher numbers of glycated proteins and more glycation sites were identified in samples from individuals with impaired glucose tolerance and type 2 diabetes mellitus.     

Electron microscopic observation of the aggregation of membrane proteins in human erythrocyte by melittin

Human erythrocytes and erythrocyte ghost membranes were treated with native and modified melittins, up to 250 nmol/mg membrane protein. Native melittin induced aggregation of intramembranous particles (IMPs, observed by freeze-fracture electron microscopy), and created large, smooth bilayer areas devoid of IMP. The degree of IMP aggregation increased with increasing concentration of melittin, corresponding to hemolysis results. Membrane ghosts were slightly more susceptible to IMP aggregation than membranes on intact cells. The potency of inducing IMP aggregation was ranked in the order of: native melittin greater than acetylated melittin greater than succinylated melittin = 0. The concentration range of melittin which caused IMP aggregation corresponded to that which caused the immobilization of band 3 proteins as detected by measurement of rotational mobility by transient dichroism (Dufton et al. (1984) Eur. J. Biophys. 11, 17-24). Because both IMP aggregation and band 3 protein immobilization decreased with decreasing positive charge of the melittins used, the nature of melittin-protein interaction is likely to be at least in part electrostatic in the case of human erythrocyte membranes. Possible roles of IMP aggregation and the consequent creation of 'exposed' bilayer areas in the cytotoxic reaction of melittins are discussed.