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PubMed1998

Regulation of band 3 rotational mobility by ankyrin in intact human red cells.

Ankyrin mutations and combined spectrin and ankyrin deficiency are prominent features of red blood cells (RBCs) in patients with hereditary spherocytosis (HS). Band 3 is the most abundant integral protein in the human RBC membrane. Previous studies have shown that the lateral mobility, but not the rotational mobility, of band 3 is increased in RBCs from patients with severe autosomal recessive HS and selective spectrin deficiency. These observations are consistent with the steric hindrance model of lateral mobility restriction. Here we use the fluorescence photobleaching recovery and polarized fluorescence depletion techniques to measure the lateral and rotational mobility of band 3 in intact RBCs from six patients with HS, ankyrin mutations, and combined spectrin and ankyrin deficiency. As predicted by the steric hindrance model, the lateral diffusion rate of band 3 is greater in spectrin- and ankyrin-deficient RBCs than in control cells, and the magnitude of the increase correlates with the degree of spectrin deficiency. Unlike RBCs from patients with HS and selective spectrin deficiency, however, HS RBCs with ankyrin mutations exhibit a marked increase in band 3 rotational diffusion. The magnitude of the increase correlates inversely with the ankyrin/band 3 ratio and with the fraction of band 3 retained in the membrane skeleton following detergent extraction. These data suggest that ankyrin deficiency relaxes rotational constraints on the major (slowly rotating) population of band 3 molecules. Increases in band 3 rotation could be due to release of band 3 from low-affinity binding sites on ankyrin.

Anion Exchange Protein 1, Erythrocyte↗
PubMedDate not supplied

Spectrofluorometric and microcalorimetric study of the thermal poration relevant to the mechanism of thermohaemolysis.

This study sheds light on the structural changes in erythrocyte membrane during thermally induced poration, an event involved in thermohaemolysis. Two major membrane disturbing events can be induced during transient heating, the denaturation of spectrin and thermoporation. The first one precedes the latter but is not involved in it. Ethanol linearly reduces the onset temperature of both events but with different efficiencies. Thermoporation efficiency exceeds by 3.5 fold that of spectrin denaturation. Thus, at a specific concentration of ethanol (18% v/v), the poration occurs at 39.5 degrees C, which precedes the denaturation of spectrin by 6 degrees C. To induce and study the poration avoiding spectrin denaturation, cells were put in contact with preheated (39 degrees C) isotonic (60mM) NaCl) media containing 18% v/v ethanol and sucrose as an osmotic protectant. After 3 min heating, the porated cells were washed, their membranes isolated and studied. The control cells were processed similarly except that they were incubated at 23 degrees C, thus avoiding thermoporation. Using scanning microcalorimetry, the enthalpy and the temperature of denaturation of spectrin were found to be the same in control as well as in porated membranes which indicates similar spectrin structure in both membranes. While the enthalpy of denaturation of the anion channel was preserved, its denaturation temperature was lowered by 2.5 degrees C after poration. These results confirmed that the heat denaturation of the main membrane proteins was not needed and not involved in thermoporation and, hence, in thermohaemolysis. Analysis of the fluorescence of membrane bound ANS gave an apparent increase in the number of binding sites for ANS in membranes after poration. In relation to the control, the eximerization of pyrene in porated membranes changed, depending on the location of the probe: in the domain of free lipids it decreased by 18% but it increased by 60% in the lipid milieu proximal to membrane proteins. Likewise, the eximerization of N-(3-Pyrene) maleimide bound to membrane proteins increased by 67% after poration, which proves increased intramolecular mobility of proteins following poration. The maximal efficiency for transferring energy from tryptophans to neighbouring pyrene was determined to be 0.93 in control, which is almost the same as in intact membranes, and 0.70 in porated membranes, indicating a strong decrease in the lipid/protein contact zone. This data suggests a mild conformational change, possibly an irreversible perturbance of the transbilayer distribution of membrane proteins in porated membranes in comparison to the control and intact ones.

Calorimetry↗
PubMed1987

Structural and functional relationship of red blood cell protein 4.1 to synapsin I.

It has been suggested that the neuron specific protein synapsin I is closely related to red blood cell (rbc) protein 4.1. A systematic comparison of the structural and functional properties of rbc protein 4.1 and synapsin I has been carried out. There is approximately a three order of magnitude difference in cross reactivity of synapsin I with rbc 4.1 antiserum vs. synapsin I antiserum, as determined by a competitive quantitative dot assay. Two-dimensional chymotryptic iodopeptide mapping analysis demonstrated limited peptide homology (approximately 34% spot overlap) between rbc 4.1 and synapsin I. Dephosphorylated synapsin I binds saturably to brain spectrin (240/235) with an estimated dissociation constant (Kd) of 700 nM and a maximal binding capacity of 4 mol synapsin I/mol spectrin tetramer, similar to the affinity and stoichiometry of 4.1 binding to rbc spectrin. Synapsin I was found to bind to the terminal ends of the brain spectrin tetramer by low-angle rotary shadowing, analogous to 4.1 binding to rbc spectrin. In summary, synapsin I is structurally and immunologically distinct from rbc 4.1, yet shares functional similarities with rbc 4.1 with respect to its spectrin binding characteristics.

Animals↗
PubMedDate not supplied

Structural determinants of the rigidity of the red cell membrane.

Although the stability and viscoelasticity of the red cell membrane are undoubtedly governed by the membrane's underlying protein skeleton, the mechanism by which this network controls elasticity is uncertain. The structural constraints, that impose end-to-end spacing on the spectrin molecules well below that in free solution, may impart rubbery (entropic) elasticity to the system. However, other enthalpic and entropic contributions due to interactions between spectrin chains or between spectrin and other proteins, the lipid bilayer or the solvent must also prevail. To relate structural features to elasticity, explicit measurements of membrane rigidity are required. The most widely used measurement is that of the membrane shear elastic modulus by micropipette aspiration. Analysis of genetic variants of membrane structure have shown that the density of spectrin is directly correlated with membrane rigidity. Although cross-linking of the skeleton increases rigidity, interruption of the continuity of the network by dissociating spectrin tetramers into dimers does not reduce rigidity as might be expected. On the other hand, external ligands that cause new interactions between integral proteins and the skeletal network do increase rigidity. Moreover, hereditary ovalocytes, which have a deletion of 9 amino acids from band 3 at the first point of entry into the membrane, are extremely rigid. This mutation is associated with decreased translational and rotational mobility of the band 3, and may impair flexural freedom of its cytoplasmic domain. It thus appears that elasticity may be regulated not only by the structure of the spectrin network, but also by its interactions with and freedom of motion relative to the lipid bilayer.

Chemical Phenomena↗
PubMed1989

[Molecular pathology of the erythrocyte membrane. Erythrocyte membrane defects as a cause of congenital hemolytic anemia].

Recently numerous defects of erythrocyte membrane proteins have been described in hereditary hemolytic anemias. An exact biochemical characterization of some different types of hereditary spherocytosis, hereditary elliptocytosis, hereditary pyropoikilocytosis and the hemolytic anemias with increased cation permeability (hereditary stomatocytosis) is possible after analysis of membrane proteins with SDS-polyacrylamide gel electrophoresis, quantitative determination of spectrin, the relation of dimeric to tetrameric spectrin, and partial tryptic digestion of the spectrins. The known clinical heterogeneity of the mentioned disorders is now partially explained by the different biochemical defects of the erythrocyte membrane. In classical hereditary spherocytosis a close relationship between erythrocyte spectrin content and clinical severity has been found. The clinical manifestation in hereditary elliptocytosis and hereditary pyropoikilocytosis mainly depends on the functional disturbance of variant spectrins, especially their ability to form tetramers, i.e. their ability for self-association of the spectrin chains. In the hydrocytic form of stomatocytosis a deficiency of the integral protein band 7.2b has been documented. Besides the analysis of erythrocyte membrane proteins the classical methods used in the study of congenital hemolytic anemias cannot be missed. Signs of increased hemolysis, erythrocyte morphology, osmotic fragility, autohemolysis, heat and mechanical stability of the erythrocyte membrane, intracellular cation concentration and studies of other family members, are indispensable prerequisites for classification, prognosis, and indication of therapeutic efforts, especially splenectomy.

Anemia, Hemolytic, Congenital↗
PubMed1994

An SH3 binding region in the epithelial Na+ channel (alpha rENaC) mediates its localization at the apical membrane.

The amiloride-sensitive Na+ channel constitutes the rate-limiting step for Na+ transport in epithelia. Immunolocalization and electrophysiological studies have demonstrated that this channel is localized at the apical membrane of polarized epithelial cells. This localization is essential for proper channel function in Na+ transporting epithelia. In addition, the channel has been shown to associate with the cytoskeletal proteins ankyrin and alpha-spectrin in renal epithelia. However, the molecular mechanisms underlying the cytoskeletal interactions and apical membrane localization of this channel are largely unknown. In this study we show that the putative pore forming subunit of the rat epithelial (amiloride-sensitive) Na+ channel (alpha ENaC) binds to alpha-spectrin in vivo, as determined by co-immunoprecipitation. This binding is mediated by the SH3 domain of alpha-spectrin which binds to a unique proline-rich sequence within the C-terminal region of alpha rENaC. Accordingly, the C-terminal region is sufficient to mediate binding to intact alpha-spectrin from alveolar epithelial cell lysate. When microinjected into the cytoplasm of polarized primary rat alveolar epithelial cells, a recombinant fusion protein containing the C-terminal proline-rich region of alpha rENaC localized exclusively to the apical area of the plasma membrane, as determined by confocal microscopy. This localization paralleled that of alpha-spectrin. In contrast, microinjected fusion protein containing the N-terminal (control) protein of alpha rENaC remained diffuse within the cytoplasm. These results suggest that an SH3 binding region in alpha rENaC mediates the apical localization of the Na+ channel. Thus, cytoskeletal interactions via SH3 domains may provide a novel mechanism for retaining proteins in specific membranes of polarized epithelial cells.

Amino Acid Sequence↗
PubMed1995

Hsp70 translocates into a cytoplasmic aggregate during lymphocyte activation.

The percentage of T and B lymphocytes expressing a distinct cytoplasmic aggregate enriched in spectrin, ankyrin, and in several other proteins including protein kinase C greatly increases following various activation protocols. Members of the 70 kDa family of heat shock proteins (hsp70) temporarily bind to and stabilize unfolded segments of other proteins, a function apparently required for proper protein folding and assembly. Considering the multiprotein and dynamic nature of the lymphocyte aggregate, the possibility that hsp70 also might be associated with components of this structure is considered here. Double immunofluorescence analysis indicates that hsp70 is a component of the lymphocyte aggregate and is coincident with spectrin in a subpopulation of freshly isolated, untreated lymphocytes from various murine tissues and in a T-lymphocyte hybridoma. When cell lysates of lymph node T cells are immunoprecipitated using an antibody against hsp70 or spectrin and then analyzed by Western blot utilizing the alternate antibody, it was found that hsp70 and spectrin coprecipitated with one another. Moreover, this coprecipitation could be abolished by addition of ATP. This latter observation was extended to lymphoid cells using a transient permeabilization procedure, and it was shown that addition of exogenous ATP results in the dissipation of the aggregate structure itself. Finally, conditions that result in T-cell activation and aggregate formation, i.e., treatment with the phorbol ester PMA or T-cell receptor cross-linking, also lead to the repositioning of hsp70 into the aggregate from a membrane/cytosolic locale in congruence with spectrin. These data suggest that hsp70 is an active component of the aggregate and that it may function in the interactions believed to occur in this unique activation-associated organelle.

Adenosine Triphosphate↗
PubMed1978

Triton shells of intact erythrocytes.

About 40% of human erythrocyte membrane protein is resistant to solubilization in 0.5% Triton X-114. These components comprise a structure called a Triton shell roughly similar in size and shape to the original erythrocyte and thus constitute a cytoskeleton. With increasing concentrations of Triton the lipid content of the Triton shell decreases dramatically, whereas the majority of the protein components remain constant. Exceptions to this rule include proteins contained in band 3, the presumed anion channel, and in band 4 which decrease with increasing Triton concentration. The Triton-insoluble complex includes spectrin (bands 1 and 2), actin (band 5), and bands 3' and 7. Component 3' has an apparent molecular weight of 88,000 daltons as does 3; but unlike 3, it is insensitive to protease treatment of the intact cell, has a low extinction coefficient at 280 nm, and is solubilized from the shells in alkaline water solutions. Component 7 also has a low extinction coefficient at 280 nm. Spectrin alone is solubilized from the Triton shells in isotonic media. The solubilized spectrin contains no bound Triton and coelectrophoreses with spectrin eluted in hypotonic solutions from ghosts. Electron micrographs of fixed Triton shells stained with uranyl acetate show the presence of numerous filaments which appear beaded and are 80--120 A in diameter. The filaments cannot be composed mainly af actin, but enough spectrin is present to form the filaments. Triton shells may provide an excellent source of material useful in the investigation of the erythrocyte cytoskeleton.

Actins↗
PubMed2001

Posterior midgut epithelial cells differ in their organization of the membrane skeleton from other drosophila epithelia.

In epithelial cells, the various components of the membrane skeleton are segregated within specialized subregions of the plasma membrane, thus contributing to the development and stabilization of cell surface polarity. It has previously been shown that, in various Drosophila epithelia, the membrane skeleton components ankyrin and alphabeta-spectrin reside at the lateral surface, whereas alphabeta(H)-spectrin is restricted to the apical domain. By use of confocal immunofluorescence microscopy, the present study characterizes the membrane skeleton of epithelial cells in the posterior midgut, leading to a number of unexpected results. First, ankyrin and alphabeta-spectrin are not detected on the entire lateral surface but appear to be restricted to the apicolateral area, codistributing with fasciclin III at smooth septate junctions. The presumptive ankyrin-binding proteins neuroglian and Na(+),K(+)-ATPase, however, do not colocalize with ankyrin. Second, alphabeta(H)-spectrin is enriched at the apical domain but is also present in lower amounts on the entire lateral surface, colocalizing apicolaterally with ankyrin/alphabeta-spectrin. Finally, despite the absence of zonulae adherentes, F-actin, beta(H)-spectrin, and nonmuscle myosin-II are enriched in the midlateral region. Thus, the model established for the organization of the membrane skeleton in Drosophila epithelia does not hold for the posterior midgut, and there is quite some variability between the different epithelia with respect to the organization of the membrane skeleton.

Animals↗
PubMed2001

Erythrocyte membrane and cytoskeletal protein glycation and oxidation in short-term diabetic rabbits.

The objective of this study was to elucidate the glycation and oxidation processes in plasma and erythrocyte membrane proteins as well as the major erythrocyte cytoskeletal protein, spectrin, using a short-term experimental rabbit diabetes model. Diabetes was induced with a single-dose alloxan injection. Spectrin was purified from erythrocyte ghosts with selective solubilization followed by gel filtration chromatography techniques, and tested for purity using sodium dodecyl sulfate-poly-acrylamide gel electrophoresis. Glycation in plasma proteins was measured as fructosamine using the nitroblue tetrazolium method, and in erythrocyte membrane and purified spectrin, as ketoamine equivalents, by the hydrazine/phenylhydrazine method. Protein oxidation in plasma, erythrocyte membrane proteins, and purified spectrin was evaluated in terms of sulfhydryl oxidation, based on cis-dichlorodiammine platinum (II) binding. Carbonyl formation was also measured in plasma and membrane proteins. Sulfhydryl oxidation, carbonyl groups and glycated protein levels showed statistically significant differences between the diabetic and control groups for both the plasma and the erythrocyte membrane proteins. The cis-dichlorodiammine platinum (II) binding was significantly different in diabetic rabbit erythrocyte spectrin, while glycation was not significantly different for this protein. Our data clearly demonstrate that both protein glycation and oxidation are biochemical alterations occurring in diabetes, even of short duration.

Animals↗
PubMed1980

Reactions of the alkylating agent tris(2-chloroethyl)-amine with the erythrocyte membrane. Effects on shape changes of human erythrocytes and ghosts.

The influence of tris(2-chloroethyl)amine on shape changes of human erythrocytes and ghosts was studied in vitro and correlated with alterations in the molecular structure of the membrane. (1) Reaction with 1--2 mM tris(2-chloroethyl)amine, a concentration which caused polymerisation of spectrin as detected by sodium dodecyl sulphate polyacrylamide gel electrophoresis, protected intact erythrocytes against metabolically induced shape changes. (2) When induced by Mg2+-ATP, ghosts porepared from alkylated erythrocytes underwent normal changes in shape. However, when ghosts were treated directly with tris(2-chloroethyl)amine, no Mg2+-ATP-induced shape changes occurred. This fixation in shape appeared to be due to a higher degree of reaction with the alkylating agent. (3) The amount of chlorpromazine necessary for transformation of erythrocytes into stomatocytes was increased for tris(2-chloroethyl)amine-pretreated cells and was dependent on the degree of reaction with tris(2-chloroethyl)amine. (4) Deformability of red cells after reaction with tris(2-chloroethyl)amine was estimated by measuring their rheological behaviour in glass capillary arrays. A slight reduction of the flow rate was observed for cells alkylated with 1--2 mM tris(2-chloroethyl)amine. (5) Extractability of spectrin was diminished and corresponded to the degree of spectrin polymerisation. (6) No difference in the incorporation of 32P by alkylated and untreated cells was found. Sodium dodecyl sulphate polyacrylamide gel electrophoresis and autoradiography of the membrane proteins from 32-P-treated cells showed that the spectrin component 2 and the polymerisation products generated by the reaction with tris(2-chloroethyl)amine were labelled. It is suggested that the observed conservation of cell shape is preferentially caused by the reaction of tris(2-chloroethyl)amine with spectrin.

Alkylating Agents↗
PubMed1980

Interaction of divalent cations with human red cell cytoskeletons.

The binding of Ca2+ to spectrin from human erythrocytes was investigated by equilibrium dialysis, and the binding of Mn2+ by electron paramagnetic resonance. The results led to the conclusion that no binding sites of high affinity (greater than about 10(4) M-1) are present. In the cytoskeletal protein complex isolated from erythrocytes, which (like crude spectrin) contains actin and some other proteins, a set of sites with an association constant of 4 x 10(4) M-1 for Mn2+ is observed. These may be divalent cation binding sites on the actin molecules. Weak interactions of Ca2+ and Mg2+ with spectrin are reflected by self-association of the spectrin heterodimers, which can be followed in the analytical ultracentrifuge and by light-scattering. This self-association is affected by the state of the protein thiol groups. Conditions in which self-association of spectrin occurs have been defined. No aggregation is observed at the Mg2+ activity thought to correspond to that in the cytoplasm.

Absorption↗
PubMed1981

Photodynamic protein cross-linking.

Exposure of spectrin to visible light in the presence of a photosensitizer results in photo-oxidation of sensitive amino acid residues and covalent cross-linking of the polypeptides. In a previous paper the cross-linking was ascribed to a secondary reaction between photo-oxidized histidine residues and amino groups. The following observations, described in this paper, are in accordance with this supposition. (1) During illumination of spectrin in the presence of a photosensitizer a pronounced photo-oxidation of histidine residues takes place. (2) Simultaneously a decrease of free amino groups is observed. (3) Semicarbazide protects against cross-linking and is bound to a histidine photo-oxidation product in spectrin. (4) The pH profile of histidine photo-oxidation and subsequent reaction with amino groups is similar to the pH profile of spectrin cross-linking. Amidination of NH2 groups in spectrin does not inhibit cross-linking, as visualized by gel electrophoresis. On the other hand aminidation of denatured myoglobin causes a 50% inhibition of cross-linking. These observations support the notion of NH2-involvement in cross-linking but also demonstrate, that other photodynamic cross-link mechanisms exist.

Amino Acids↗
PubMed1994

Calcium-activated proteolysis in rat neocortex induced by transient focal ischemia.

Ischemia-induced elevation of intracellular calcium triggers a cascade of events which is considered to play a major role in neuronal death. One candidate to participate in this process is the calcium-sensitive protease, calpain. This protease is activated by calcium, and is capable of degrading critical cytoskeletal and regulatory proteins. In order to further elucidate the role of calpain in focal ischemic damage, the present study investigated the proteolysis of spectrin, a preferred substrate for calpain, in response to transient focal ischemia. Ischemia was induced by occluding reversibly both carotid arteries and the left middle cerebral artery for three hours in Sprague-Dawley rats. Western blotting techniques were used to identify and quantify the amounts of spectrin breakdown products (BDPs) in neocortical samples from the area destined for infarction, the peri-infarct area, and the contralateral hemisphere. Substantial increases in spectrin proteolysis were observed within the first few hours of ischemia in the areas that will undergo infarction. The increase in spectrin BDPs in these areas reached a plateau around the end of the 3 h ischemic period. In the peri-infarct zone, the levels of spectrin BDPs increased in a biphasic manner. A small to moderate increase was observed by the second hour of ischemia, followed by a larger increase between the 6th and 24th hours post-ischemia. The contralateral neocortex showed a significant increase in BDPs at 2 h after the initiation of ischemia. A smaller increase in BDPs was observed thereafter.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed1979

Molecular changes in the membranes of mouse erythroid cells accompanying differentiation.

The development of the mouse erythroblast to a mature erythrocyte is accompanied by changes in the composition and properties of the plasma membranes of these cells. Using double fluorescence techniques, we have simultaneously determined the distribution of lectin receptors and spectrin on the membranes of these cells. The lateral mobility of the lectin receptors in the membranes decreases as differentiation proceeds, and this is accompanied by an increasing concentration of spectrin associated with the membranes. The most significant concentration of spectrin occurs, however, during the enucleation of the late erythroblast, where we observe a complete segregation of the spectrin to the incipient reticulocyte, as well as a previously observed enrichment of receptors for concanavalin A into the plasma membrane surrounding the extruding nucleus. On the basis of these and other observations, we explore the possible molecular mechanisms involved in erythroblast enucleation and the role of spectrin in the regulation of protein mobility in erythroid cell membranes.

Actins↗
PubMed2005

Cooperative folding in a multi-domain protein.

Most protein domains are found in multi-domain proteins, yet most studies of protein folding have concentrated on small, single-domain proteins or on isolated domains from larger proteins. Spectrin domains are small (106 amino acid residues), independently folding domains consisting of three long alpha-helices. They are found in multi-domain proteins with a number of spectrin domains in tandem array. Structural studies have shown that in these arrays the last helix of one domain forms a continuous helix with the first helix of the following domain. It has been demonstrated that a number of spectrin domains are stabilised by their neighbours. Here we investigate the molecular basis for cooperativity between adjacent spectrin domains 16 and 17 from chicken brain alpha-spectrin (R16 and R17). We show that whereas the proteins unfold as a single cooperative unit at 25 degrees C, cooperativity is lost at higher temperatures and in the presence of stabilising salts. Mutations in the linker region also cause the cooperativity to be lost. However, the cooperativity does not rely on specific interactions in the linker region alone. Most mutations in the R17 domain cause a decrease in cooperativity, whereas proteins with mutations in the R16 domain still fold cooperatively. We propose a mechanism for this behaviour.

Amino Acid Sequence↗
PubMed2004

Effects of fimbria-fornix transection on calpain and choline acetyl transferase activities in the septohippocampal pathway.

The ability of fimbria-fornix bilateral axotomy to elicit calpain and caspase-3 activation in the rat septohippocampal pathway was determined using antibodies that selectively recognize either calpain- or caspase-cleaved products of the cytoskeletal protein alphaII-spectrin. Radioenzymatically determined choline acetyl transferase (ChAT) activity was elevated in the septum at day 5, but reduced in the dorsal hippocampus at days 3, 5 and 7, after axotomy. Prominent accumulation of calpain-, but not caspase-3-, cleaved spectrin proteolytic fragments was observed in both the septum and dorsal hippocampus 1-7 days after axotomy. ChAT-positive neuronal cell bodies in the septum also displayed calpain-cleaved spectrin indicating that calpain activation occurred in cholinergic septal neurons as a consequence of transection of the septohippocampal pathway. Calpain-cleaved alphaII-spectrin immunoreactivity was observed in cholinergic fibers coursing through the fimbria-fornix, but not in pyramidal neurons of the dorsal hippocampus, suggesting that degenerating cholinergic nerve terminals were the source of calpain activity in the dorsal hippocampus following axotomy. Accumulation of calpain-cleaved spectrin proteolytic fragments in the dorsal hippocampus and septum at day 5 after axotomy was reduced by i.c.v. administration of two calpain inhibitors. Calpain inhibition partially reduced the elevation of ChAT activity in the septum produced by transection but failed to decrease the loss of ChAT activity in the dorsal hippocampus following axotomy. These findings suggest that calpain activation contributes to the cholinergic cell body response and hippocampal axonal cytoskeletal degradation produced by transection of the septohippocampal pathway.

Animals↗
PubMed1992

Gaps in the erythrocyte membrane skeleton: a stretched net model.

The geometry of spectrin-free regions in the erythrocyte membrane skeleton is modeled using Monte Carlo calculations for an incomplete triangular lattice of entropy springs under tension. Intact springs correspond to normal spectrin molecules, and cut springs correspond to spectrin that is missing or unable to associate normally. As springs are cut and the network is allowed to relax to mechanical equilibrium, gaps in the network appear. Geometrical properties of these gaps are obtained as a function of the fraction of springs cut. The most important property modeled is the area of the largest spectrin-free region; this area increases approximately exponentially as the fraction of normal spectrin decreases from 100% to approximately 50%. The effect of these gaps on lateral diffusion and vesiculation is discussed.

Erythrocyte Membrane↗