Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Spectrin”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 613 records · Page 34Linked to original sources
PubMed1982

Widespread occurrence of avian spectrin in nonerythroid cells.

We have prepared an antibody against chicken erythrocyte alpha spectrin, using as immunogen protein purified by two-dimensional polyacrylamide gel electrophoresis. One- and two-dimensional immunoautoradiography show that this antiserum reacts only with alpha spectrin in chicken erythrocytes and crossreacts with alpha spectrin in erythrocytes from various mammals. Immunofluorescence reveals that this antiserum reacts with a plasma membrane component in erythrocytes as well as in most nonerythroid avian and mammalian cells. Intense staining is seen at or near the plasma membrane in neurons, lens cells, endothelial and epithelial cells of the gastrointestinal and respiratory tracts, skeletal and cardiac muscle, as well as skeletal myotubes grown in tissue culture. Immunoautoradiography indicates that the crossreactive antigen in these nonerythroid tissues has the same molecular weight and isoelectric point as the chicken erythrocyte antigen. Smooth muscle, tracheal cilia, myelin and mature sperm stain weakly or not at all. These results suggest that spectrin is more extensively distributed than previously recognized, and that the functions of spectrin elucidated for erythrocytes may apply to other cell types as well.

Animals↗
PubMed1989

Conformational stability of spectrin and fodrin.

The conformational stability of erythrocyte spectrin and brain spectrin-like protein (fodrin) has been studied by circular dichroism. In agreement with previous reports the circular dichroism spectra of both proteins in the peptide region were almost identical. The essential differences, on the other hand, were found in the near u.v. range, most probably due to differences in the conformation of intrachain disulphide bonds. Heat denaturation curves, relating to the level of secondary structure (ellipticity at 221 nm) showed that fodrin is more stable than spectrin: curves of reversible as well as irreversible denaturation are shifted to higher temperatures and also the amount of alpha-helices in the denatured state is higher. Spectrin conformation was found to be very sensitive to the presence of water-soluble organic solvents; the denaturation curves exhibit maxima and minima not typical of protein isothermic denaturation. The observed low conformational stability of spectrin is discussed in the context of its molecular environment and function in the red cell membrane.

Animals↗
PubMed1991

The ring-infected erythrocyte surface antigen of Plasmodium falciparum associates with spectrin in the erythrocyte membrane.

The malaria parasite Plasmodium falciparum synthesises a protein, RESA, which associates with the membrane of newly invaded erythrocytes. Using spent supernatants from P. falciparum growing in culture as a source of soluble RESA we have developed an assay to examine the characteristics of RESA binding to the erythrocyte membrane in vitro. RESA associated with the Triton X-100 insoluble proteins on the inner face of the host erythrocyte membrane but did not bind to the outer surface of intact erythrocytes. Other proteins present in culture supernatants did not bind to the erythrocyte membrane. RESA was co-sedimented with the ternary complex formed between actin, spectrin and band 4.1 and co-precipitated with spectrin precipitated with anti-spectrin antibodies. The extent of association between RESA and the inner face of the erythrocyte membrane was reduced by the inclusion of excess purified spectrin in the assay. Thus, RESA appears to be associated with spectrin in the erythrocyte membrane skeleton.

Animals↗
PubMed1986

Binding of complement component C1q by spectrin.

125I-labelled human C1q was found to bind to human spectrin. Scatchard plots for the binding process were non-linear, indicating the possible presence of multiple classes of binding sites for C1q on spectrin. The binding was ionic-strength-dependent; the extent of binding decreased with increasing ionic strength. Chemical modification of arginine and histidine residues on C1q as well as pretreatment of C1q at pH 4.45 or at 56 degrees C reduced its spectrin binding activity. The amount of 125I-labelled C1q bound to immune complexes was reduced by the presence of spectrin. Spectrin was also able to deplete the complement haemolytic activity of human serum in a dose-dependent manner.

Complement Activating Enzymes↗
PubMed1984

Interaction between microtubule-associated protein tau and spectrin.

Tau factor, one of the microtubule-associated proteins (MAPs), is shown here to bind to spectrin. Evidence for an interaction between these two proteins is provided by spectrin affinity chromatography of brain MAPs, gel overlay of electrophoresed MAPs with 125I-labelled spectrin, incorporation of tau factor in human erythrocyte ghosts, and demonstration that tau inhibits the F-actin cross-linking activity of tetrameric spectrin. The wide distribution of both tau and spectrin-like proteins in eukaryotic cells is in favor of the possible biological significance of this interaction. The results suggest that tau could be one of the proteins involved in the concerted regulation of microtubule and actin networks in the membrane vicinity.

Actins↗
PubMed1994

The concentration dependence of the activity coefficient of the human spectrin heterodimer. A quantitative test of the Adams-Fujita approximation.

The heterodimer and tetramer states of human spectrin, in equilibrium at 30 degrees C, have been resolved by means of sedimentation velocity experiments at low temperature. This has allowed quantification of the concentrations of each oligomer at equilibrium, as a function of the total concentration of spectrin. In separate sedimentation equilibrium experiments, the thermodynamic activity of the heterodimer has been estimated as a function of the total spectrin concentration through the use of the Omega function. Combination of the concentration and thermodynamic activity of the spectrin heterodimer allowed estimation of the activity coefficient of the heterodimer as a function of total spectrin concentration. Over the accessible concentration range of 0-16 g/L, the logarithm of the activity coefficient of the heterodimer was linear in the total concentration, and the apparent equilibrium constant for tetramer formation was only weakly dependent on concentration, implying that a single virial coefficient is sufficient to describe the nonideality of this system over this concentration range.

Humans↗
PubMed1994

A proton nuclear magnetic resonance study of the mobile regions of human erythroid spectrin.

The effect of added NaCl (0-150 mM) and temperature (6-65 degrees C) on the conformation of erythrocyte spectrin was investigated using 400 MHz 1H NMR. The relatively narrow resonances (20-40 Hz linewidth) in the spectra arising from protons in regions of the molecule undergoing rapid motions were selectively detected using either the Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence without water presaturation or a simple pi/2 pulse sequence with water presaturation. The T2 relaxation of these protons was not influenced by changes in solution conditions (0-150 mM NaCl, 6-37 degrees C) indicating that their motions were independent of the overall shape of the molecule. Significant increases in the areas of the aliphatic peaks for spectrin samples at fixed salt concentrations occurred as the temperature was raised from 6 to 37 degrees C. The increases were independent of the state of polymerization of spectrin and were greater in the absence of added salt above 25 degrees C. The changes reflect increasing numbers of mobile residues, probably due to partial unfolding of spectrin's repeated structural unit. At temperatures above 37 degrees C, sharp increases in the areas of the spectral envelopes reflect cooperative unfolding of spectrin. Comparison with results previously obtained in this laboratory using CD and ORD indicate that at least part of the lost structure is alpha-helical.

Erythrocytes↗
PubMed1996

Assessment of the validity of the Adams and Fujita approximation for the higher oligomers of human spectrin.

Analysing the self-association behaviour of human erythrocyte spectrin is complicated by a large degree of nonideality. Adams and Fujita [1] proposed that, as a first order approximation, the logarithm of the activity coefficient of the protomer of a self-associating system can be considered to be linearly dependent on the total concentration of the protein, and that the same second virial coefficient could be considered to apply to all species. As a consequence of the Adams and Fujita approximation, the apparent equilibrium constant is equal to the thermodynamic equilibrium constant. The equilibrium concentrations at 30 degrees C of each oligomer spectrin species up to the 14-mer were determined after electrophoresis at low temperature. An apparent equilibrium constant for forming tetramer (K2,4) of (1.2 +/- 0.1) x 10(6) 1/mol was obtained, a value of (9.4 +/- 0.7) x 10(4) 1/mol was obtained for K4.6 and for all reactions forming oligomers higher than the hexamer an average approximate value of (2.7 +/- 0.4) x 10(5) 1/mol was obtained. The apparent equilibrium constants for the formation of all oligomer species of spectrin up to the tetrakaidecamer (14-mer) remain relatively independent of total spectrin concentration, and indicate that within the precision of the measurements a single virial coefficient is sufficient to account for the nonideality of spectrin self-association over the range 2-14 g/l, thus further justifying the use of the Adams and Fujita approximation for this protein over this concentration range.

Electrophoresis↗
PubMed1987

Brain spectrin, calpain and long-term changes in synaptic efficacy.

This chapter discusses the possibility that proteolytic digestion of cytoskeletal proteins, in particular spectrin, is part of the mechanisms through which physiological activity elicits structural and chemical changes in brain synapses. Recent work from several laboratories has produced a description of the initial events that trigger the long-term potentiation (LTP) of synaptic responses that appears in hippocampus after brief episodes of high frequency electrical stimulation. A likely sequence is as follows: suppression of IPSPs, prolongation of EPSPs, activation of N-methyl-D-aspartate (NMDA) receptors, influx of calcium into target cells. After briefly describing the evidence for this triggering sequence, the review takes up the question of what types of calcium sensitive chemistries are available to synaptic region that could produce functional changes lasting for weeks (i.e., for LTP). It is argued that the partial degradation of spectrin by a calcium-activated protease (calpain) provides a mechanism of this type. Spectrin is a substrate for calpain and both it and a breakdown product comparable to that produced by calpain are found in postsynaptic densities. Moreover, there is substantial evidence that spectrin regulates the surface chemistry and morphology of cells and thus its partial degradation would be expected to produce pronounced and persistent modifications in synapses. To reinforce this point, the review discusses recent findings suggesting that calpain mediated proteolysis of spectrin and other cytoskeletal proteins produces substantial changes in the shape of blood-borne cells and the distribution of their surface receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Sequence comparison of human and murine erythrocyte alpha-spectrin cDNA.

The results of hybridization analyses using cDNA probes for mouse and human alpha-spectrin mRNA indicate that a single gene encodes the alpha-subunit of erythrocyte spectrin. Sequencing of the cDNA clones showed that they code for 370 amino acids (aa) covering three repeat domains close to the C terminus of alpha-spectrin. The cloned cDNAs will now permit the isolation of the alpha-spectrin gene and should lead to the characterization of the genetic aspects in human hereditary anemias in which alpha-spectrin has been characterized as the site of the molecular defect.

Animals↗
PubMed2005

Phospholipid binding by proteins of the spectrin family: a comparative study.

Erythroid and neuronal spectrin (fodrin) are both known to interact strongly with the aminophospholipids that occur in the inner leaflet of plasma membranes. In erythroid spectrin the positions of the binding sites within the constituent (alphaI and betaI) polypeptide chains have been defined, and also the importance of the lipid interaction in regulating the properties of the membrane. Here we report the locations of the corresponding binding sites in the alphaII and betaII chains that make up the fodrin molecule. Of the 10 lipid-binding repeats in the erythroid spectrin chains 5 are conserved in fodrin; one cluster of 3 consecutive structural repeating units in alphaI erythroid spectrin (repeats 8-10) is displaced by one repeat in alphaII fodrin (repeats 9-11). Fodrin also contains one binding site at the N-terminus of the alphaII chain, not present in the erythroid protein. The regions of the two spectrins containing equivalent lipid-binding sites show a much higher degree of sequence identity than corresponding repeats that do not share this property. The evolutionary conservation of the distribution of a large proportion of strong lipid-binding sites in the polypeptide chains of these two proteins of disparate character argues for a specific function of fodrin-phospholipid interactions in the neuron.

Amino Acid Sequence↗
PubMed2005

Presynaptic spectrin is essential for synapse stabilization.

BACKGROUND: Precise neural circuitry is established and maintained through a regulated balance of synapse stabilization and disassembly. Currently, little is known about the molecular mechanisms that specify synapse stability versus disassembly. RESULTS: Here, we demonstrate that presynaptic spectrin is an essential scaffold that is required to maintain synapse stability at the Drosophila neuromuscular junction (NMJ). Loss of presynaptic spectrin leads to synapse disassembly and ultimately to the elimination of the NMJ. Synapse elimination is documented through light-level, ultrastructural, and electrophysiological assays. These combined assays reveal that impaired neurotransmission is secondary to synapse retraction. We demonstrate that loss of presynaptic, but not postsynaptic, spectrin leads to the disorganization and elimination of essential synaptic cell-adhesion molecules. In addition, we provide evidence of altered axonal transport and disrupted synaptic microtubules as events that contribute to synapse retraction in animals lacking presynaptic spectrin. CONCLUSIONS: Our data suggest that presynaptic spectrin functions as an essential presynaptic scaffold that may link synaptic cell adhesion with the stabilization of the underlying microtubule cytoskeleton.

Animals↗
PubMed2004

Structural insights into the stability and flexibility of unusual erythroid spectrin repeats.

Erythroid spectrin, a major component of the cytoskeletal network of the red cell which contributes to both the stability and the elasticity of the red cell membrane, is composed of two subunits, alpha and beta, each formed by 16-20 tandem repeats. The properties of the repeats and their relative arrangement are thought to be key determinants of spectrin flexibility. Here we report a 2.4 A resolution crystal structure of human erythroid beta-spectrin repeats 8 and 9. This two-repeat fragment is unusual as it exhibits low stability of folding and one of its repeats lacks two tryptophans highly conserved among spectrin repeats. Two key factors responsible for the lower stability and, possibly, its flexibility, are revealed by the structure. A third novel feature of the structure is the relative orientation of the two repeats, which increases the range of possible conformations and provides new insights into atomic models of spectrin flexibility.

Amino Acid Sequence↗
PubMed2003

Cooperativity in forced unfolding of tandem spectrin repeats.

Force-driven conformational changes provide a broad basis for protein extensibility, and multidomain proteins broaden the possibilities further by allowing for a multiplicity of forcibly extended states. Red cell spectrin is prototypical in being an extensible, multidomain protein widely recognized for its contribution to erythrocyte flexibility. Atomic force microscopy has already shown that single repeats of various spectrin family proteins can be forced to unfold reversibly under extension. Recent structural data indicates, however, that the linker between triple-helical spectrin repeats is often a contiguous helix, thus raising questions as to what the linker contributes and what defines a domain mechanically. We have examined the extensible unfolding of red cell spectrins as monomeric constructs of just two, three, or four repeats from the actin-binding ends of both alpha- and beta-chains, i.e., alpha(18-21) and beta(1-4) or their subfragments. In addition to single repeat unfolding evident in sawtooth patterns peaked at relatively low forces (<50 pN at 1 nm/ms extension rates), tandem repeat unfolding is also demonstrated in ensemble-scale analyses of thousands of atomic force microscopy contacts. Evidence for extending two chains and loops is provided by force versus length scatterplots which also indicate that tandem repeat unfolding occurs at a significant frequency relative to single repeat unfolding. Cooperativity in forced unfolding of spectrin is also clearly demonstrated by a common force scale for the unfolding of both single and tandem repeats.

Elasticity↗
PubMed1989

The spectrin network as a barrier to lateral diffusion in erythrocytes. A percolation analysis.

The spectrin network on the cytoplasmic surface of an erythrocyte can be modeled as a triangular lattice of spectrin tetramers (Tsuji, A., and S. Ohnishi, 1986. Biochemistry. 25:6133-6139). The tetramers act as barriers to protein diffusion, while dissociated dimer pairs, single dimers, and missing tetramers do not. Diffusion in the presence of these barriers is shown to be equivalent to bond percolation on the honeycomb lattice. Monte Carlo calculations for this system then yield the relative diffusion constant of a mobile integral protein as a function of the fraction of spectrin tetramers. At high concentrations of spectrin tetramer, long-range diffusion is blocked, but short-range diffusion is still possible. Monte Carlo calculations yield the average distance over which short-range diffusion can occur, as a function of the fraction of spectrin tetramers. Applications to erythrocyte development and hereditary hemolytic anemia are discussed.

Algorithms↗
PubMed2000

Spin label EPR structural studies of the N-terminus of alpha-spectrin.

Spectrin, a vital component in human erythrocyte, is composed of alpha- and beta-subunits, which associate to form (alphabeta)2 tetramers. The tetramerization site is believed to involve the alpha-spectrin N-terminus and the beta-spectrin C-terminus. Abnormal interactions in this region may lead to blood disorders. It has been proposed that both termini consist of partial structural domains and that tetramerization involves the association of these partial domains. We have studied the N-terminal region of a model peptide for alpha-spectrin by making a series of double spin-labeled peptides and studying their dipolar interaction by electron paramagnetic resonance methods. Our results indicate that residues 21-42 of the N-terminus region exhibit an alpha-helical conformation, even in the absence of B-spectrin.

Biopolymers↗
PubMed1999

Calpain-induced proteolysis of beta-spectrins.

The calcium-activated neutral protease calpain is activated in several pathological conditions. Calpain usually hydrolyses one or only a few peptide bonds in its substrate. One prominent substrate for calpain is spectrin and it has been shown that alpha-spectrin is the preferred substrate. We now show that the beta-chain of spectrin is also a substrate for calpain proteolysis, and that the cleavage site in each beta-subunit is located at the very C-terminal part of the molecule. Surprisingly, beta1sigma-spectrin is cleaved at a different site than betaIsigma2- and betaIIsigma1-spectrins despite their high degree of sequence identity.

Amino Acid Sequence↗
PubMed1999

Alpha-actinin and spectrin structures: an unfolding family story.

In red blood cells, the integrity of the spectrin network is essential for normal cell shape and elasticity. To understand the molecular basis for spectrin's mechanical properties, one must determine how spectrin subunits interact with each other. The newly described crystallographic structures of two consecutive homologous repeats of human alpha-actinin, a member of the spectrin superfamily, shed new light on alpha-actinin interchain binding properties. Here I present evidence that interchain binding at the tail end of the spectrin molecule is likely to occur via a mechanism similar to that observed for alpha-actinin.

Actinin↗