This supportive lattice on the inner aspect of the lipid bilayer gives the RBC its unique properties of strength and suppleness. The test may be normal in the presence of iron deficiency, obstructive jaundice, and increased reticulocytes. Because spectrins coordinate interactions between mem-brane proteins and actin in most polarized cells, and because in mature myelinating Schwann cells spectrins are highly polarized Spectrin is the main component of the cell membrane skeleton. Hereditary spherocytosis is a condition in which spectrin, a peripheral cytoskeletal protein, is depleted by 40-80%. Protein 4.2 is a peripheral membrane protein that helps link the skeleton to the lipid bilayer through interactions with ankyrin and band 3. Damian Silbermins M.D., Ara D. Metjian M.D., in Medical Secrets (Fifth Edition), 2012. The extent of spectrin deficiency correlates with the degree of hemolysis, changes in osmotic fragility, and response to splenectomy. Spectrin–actin–protein 4.1 assembly is secured to the overlying lipid bilayer by ankyrin. Calpain-mediated proteolysis of axonal neurofilaments and other cytoskeletal proteins has been demonstrated during wallerian degeneration and other experimental models of peripheral neuropathy.3,17,19 Although not widely appreciated, spectrin has been demonstrated to be a component of the cytoskeleton of both peripheral nerve axons and Schwann cells,9 although its function in peripheral … • Unlike peripheral proteins, integral proteins are associated with lipid when solubilized. αII-spectrin is an important component of the nucleoskelelton and has both structural and non-structural functions. Spectrin impacts neuron architecture, polarity, axon stability, axonal transport, dendritic spine activity, and mechanotransduction. These proteins do not have many exposed hydrophobic residues as integral proteins and can be easily removed from the membrane by changing pH or ionic strength. Integral and peripheral proteins are two types of membrane proteins in the phospholipid bilayer. Immunoblotting used polyclonal antibodies against protein 4.2 and monoclonal antibodies: BRIC170 (N-terminal band 3), BRIC155 (C-terminal band 3), and BRIC163 GPA. A relatively newer test is eosin-5-maleimide binding by flow cytometry. Several years later these predictions were borne out. Nonerythroid αII-spectrin is a structural protein whose roles in the nucleus have just begun to be explored. The regulatory protein subunits of many ion channels and transmembrane receptors, for example, may be defined as peripheral membrane proteins. This results in a reduced surface area-to-volume ratio and the formation of spherocytes. Laura Bonetta; Spectrin is peripheral . Disruption of the horizontal interactions of membrane skeleton proteins, including perturbation of spectrin self-association or junctional complex protein-protein interactions, leads to membrane instability, altered membrane deformability and mechanical properties, and the phenotype of elliptocytosis. It is logical to perform a direct antiglobulin test (DAT) to rule out autoimmune hemolytic anemia. Necl proteins are members of the IgCAM superfamily and Necl4 expressed in Schwann cells interacts with Necl1 on axons, thereby mediating axon–glia contact during PNS myelination ( 17 , 18 ). More recently, superresolution microscopy revealed distinct localization of spectrin within the axon compared to dendrites (Xu et al., 2013). Spectrin is localized to the inner membrane surface of red cell ghosts. For example, treatment of cultured neurons with latrunculin A, a toxin that causes depolymerization of actin by sequestering G-actin, results in a decrease in AMPA and NMDARs, α-actinin-2, drebrin (an actin-binding protein that can cluster actin), and CaMKII from spines. Importantly, αII-spectrin localizes in both the cytoplasm and the nucleus; in the nucleus it is best known for its links to Fanconi anemia (FA) since αII-spectrin provides a scaffold that helps recruit DNA repair proteins to sites of DNA damage (McMahon et al., 1999, 2001). Spectrin deficiency is the most common cause of this disorder. Specifically, interrupting the binding of β1-spectrin to NCAM with dominant negative β1-spectrin subunits 2–3 in hippocampal neurons blocked neurite outgrowth downstream of NCAM (Leshchyns’ka et al., 2003). It was a collaborative study between Singer, his then graduate student Garth Nicolson, and Vincent Marchesi of the National Institutes of Health that provided strong evidence for the existence of peripheral proteins (Nicolson et al., 1971a). 2α, 2β, and 2μ tetramerize to form an actin-crosslinking protein, with different isoforms localizing to the soma and neurite processes (Lazarides and Nelson, 1983). In erythrocytes the spectrin–actin–protein 4.1 network is responsible for elasticity and mechanical recovery after deformation (Bennett and Gilligan, 1993). The overall domain structures of spectrins from vertebrates and invertebrates are nearly identical to one another, with sequence identities in the range of 42–63%, suggesting that spectrins in different species are likely to have overlapping functions. Spectrin is localized to the inner membrane surface of red cell ghosts. An X, Mohandas N: Disorders of the red cell membrane, Br J Haematol 141:367–375, 2008. Shalini Menon, Stephanie L. Gupton, in International Review of Cell and Molecular Biology, 2016. Spectrin is the major component of the membrane skeleton. Their combined presence in the nucleus suggests similar, possibly essential, contributions to nuclear elasticity that will be important to test. So cytochrome c is a peripheral protein, that is essential for life and for health, but we never even think about it.AnchoringPeripheral membrane proteins are used to anchor the plasma membrane to the cytoskeleton. Abnormalities in any of these proteins result in deformation-induced membrane fragmentation. Fractionation of the ghosts resulted in three fractions: spectrin-actin, the peripheral proteins soluble in high salt, and the smooth membrane containing integral proteins. The degree of spectrin deficiency is reported to correlate with the extent of spherocytosis, the degree of abnormality on osmotic fragility test results, and the severity of hemolysis. Axon formation and guidance is also hindered in the absence of αII-spectrin as seen in the ventricular zone of mice genetically lacking αII-spectrin (Stankewich et al., 2011). We used stochastic optical reconstruction microscopy to study the organization of actin, spectrin, and associated proteins in neurons. Ankyrin binds to the 15th repetitive unit of erythroid and nonerythroid beta-spectrin. When spectrin was first described in neurons in 1981 it was named fodrin, because its relationship to spectrin was not yet known. Spectrin is highly flexible and assumes a variety of conformations, an unusual property that may be critical for normal membrane pliancy. Information and translations of spectrin in the most comprehensive dictionary definitions resource on … The calcium and kinase dependence of the spectrin-NMDAR interaction provides a potential mechanism by which NMDAR motility in the membrane may be regulated by synaptic activity. Patrick G. Gallagher, in Goldman's Cecil Medicine (Twenty Fourth Edition), 2012. Among the nuclear proteins that coimmunoprecipitated with αII-spectrin are actin, protein 4.1B, β-spectrin (βSpIVΣ5), lamin A, and emerin (Sridharana et al., 2006). The plasma membrane, which is also referred to as the cytoplasmic membrane, is a biological membrane that encloses the contents of the cell and separates it from the outer environment. Dubreuil, in Reference Module in Biomedical Sciences, 2015. The peripheral protein network of the red blood cell (RBC) membrane is mainly made of spectrin, actin and protein 4.1. Spectrin dimer bonds that appear along the length of the molecules disassociate and reassociate (open and close) during RBC deformation. Spectrin deficiency leads to loss of erythrocyte surface area, which produces spherical RBCs. In addition, dominant mutations in the βIII isoform of spectrin have been shown to cause spinocerebellar ataxia type 5 in humans. In the neuromuscular junction, removal of actin and spectrin from myotube membranes results in dispersal of AChRs (Bloch, 1986). Electron micrscopy (EM) analysis then localized the electron-dense ferritin-conjugated anti-spectrin antibodies specifically to the inner surface of the cell membrane (Nicolson et al., 1971a). Likewise, the 20 α-spectrin and 16 β-spectrin repeated helices unfold and refold.43 These flexible interactions plus the spectrin-protein 4.1 junctions in the actin junctional complexes between the tetramers are key regulators of membrane elasticity and mechanical stability. Spectrins form a structural unit consisting of αβ tetramers, for example, (αIβI)2 in erythrocytes. Loss of function of β-spectrin but not α-spectrin in Drosophila causes axon-guidance defects at the midline (Hulsmeier et al., 2007). Peripheral membrane proteins are used to anchor the plasma membrane to the cytoskeleton. It is composed of two subunits, α and β spectrin, that are structurally related but functionally distinct. Erythrocyte membrane disorders result from alterations in the quantity or quality (or both) of individual proteins and their dynamic interactions with each other. In the following discussion, the term spectrin will refer to the brain form of spectrin. Because spectrins contribute to the stabilization of membrane proteins, we considered whether loss of spectrin affects the membrane proteins required for axon–glia interactions or myelination. To investigate this idea, Singer wanted to see where spectrin was located. doi: https://doi.org/10.1083/jcb1701fta1. αII-Spectrin binds directly to Fanconi anemia complementary group G (FANCG) (a component of the FANCA, FANCC, FANCF, FANCG complex) and colocalizes with the cross-link repair protein, XPF, in damage-induced nuclear foci after treatment of cells with DNA interstrand cross-linking agents (Lefferts et al., 2009; Sridharana et al., 2003). Unlike integral membrane proteins , peripheral proteins do not enter into the hydrophobic space within the cell membrane . Zhixia Zhong, ... Kris Noel Dahl, in Methods in Cell Biology, 2010. Within the membrane skeleton, the α and β subunits typically form heterotetramers by forming antiparallel heterodimers that interact head to head to form a tetramer. The SPTBN4 gene encodes a nonerythrocytic member of the beta-spectrin protein family that is expressed in the brain, peripheral nervous system, pancreas, and skeletal muscle. It is now known that spectrin is the most abundant peripheral membrane protein in red blood cells and the principal component of a protein meshwork, or membrane skeleton, that underlies the cell membrane. Most cases of hereditary spherocytosis are heterozygous because homozygous states are lethal. Singer's model, however, proposed that integral membrane proteins, which passed through the membrane, would be insoluble in water. The β subunit also contains an actin-binding region at its N terminus, and some β subunits contain a PH domain. There are both autosomal dominant and recessive forms of the condition, with differing severity. Spectrin has been said to resemble, to some degree, the actin-binding protein of rabbit pulmo- This leads to membrane instability with loss of lipids and some integral membrane proteins, resulting in loss of membrane surface area and the phenotype of spherocytosis. Peripheral protein, or peripheral membrane proteins, are a group of biologically active molecules formed from amino acids which interact with the surface of the lipid bilayer of cell membranes. Dubreuil, in Encyclopedia of Neuroscience, 2009. By continuing you agree to the use of cookies. Peripheral membrane proteins are membrane proteins that adhere only temporarily to the biological membrane with which they are associated. Patients with hereditary spherocytosis develop splenomegaly. Peripheral proteins and smooth membrane from erythrocyte ghosts. While dystrophin is related to β spectrin, it appears to have evolved independently and is not known to associate with any other subunits or to form tetramers. The Spectrin Cytoskeleton Is Polarized in Premyelinating Schwann Cells. E. Marcora, ... M.B. (B) Proteins of the glycophorin C (GPC) complex, plus aquaporin 1 (AQP1) and cytoskeletal proteins spectrin and actin. The tail of spectrin tetramers binds with a protein cluster of short actin protofilaments, and this interaction is markedly enhanced by protein 4.1. The most common genetic defect in HS is in the ankyrin gene. In the axon, spectrin forms periodic ring-like structures, whereas in dendrites spectrin was organized longitudinally along F-actin within the dendritic shaft (Xu et al., 2013). Hereditary spherocytosis is the most common of the hereditary hemolytic anemias among people of northern European descent. The localization of spectrin in vertebrate neurons, and the phenotypes observed in invertebrates, suggest that the function for multiple spectrin variants is likely important in vertebrate neuronal morphogenesis. A normal osmotic fragility test does not necessarily exclude the diagnosis of hereditary spherocytosis. The principle of this test is that spherocytes will easily lyse when placed in hypotonic solution. Definition of spectrin in the Definitions.net dictionary. Its best known role is in repair of DNA ICLs both in genomic and telomeric … Spectrin is highly flexible and assumes a variety of conformations, an unusual property that may be critical for normal membrane pliancy. • Examples of peripheral proteins are spectrin of erythrocytes, cytochrome C and ATP-ase of mitochondria and acetylcholinesterase in electroplax membranes. It is now known that spectrin is the most abundant peripheral membrane protein in red blood cells and the principal component of a protein meshwork, or membrane skeleton, that underlies the cell membrane. In humans there are five known β spectrin genes and two α genes. It is transmitted as autosomal dominant, but in 25% of cases, it is due to a spontaneous mutation. Spectrins, first identified as a major component of the membrane skeleton of red blood cells (erythrocytes), are a well-characterized class of cytoskeletal proteins that line the plasma membrane. Amer Wahed MD, Amitava Dasgupta PhD, DABCC, in Hematology and Coagulation, 2015. Spherocytes are also seen in autoimmune hemolytic anemia. Search for other works by this author on: This site uses cookies. The significance of the peripheral erythrocyte membrane proteins, of which spectrin is the principle component, in maintaining the shape of the red blood cells, has recently been recognized [ 1 ,2]. Normal red blood cells are spherical. It could be isolated by mild treatments and behaved like a water-soluble protein. Spectrin deficiency is due to impaired synthesis. 9, D–F) and central (H) and peripheral (I) nodes of Ranvier. In avian erythrocytes it exists as a family of closely related polypeptides that are differentially expressed during erythropoiesis. 2α-spectrin genes and 5β-spectrin genes have been identified in mammals, each encoding multiple splice variants. LB. Kennedy, in Learning and Memory: A Comprehensive Reference, 2008. Interestingly, II spectrin is essential for the development of various organs such as β nerve, epithelium, inner ear, liver and heart. Several years later these predictions were borne out. Actin and spectrin play important roles in neurons, but their organization in axons and dendrites remains unclear. These proteins attach to integral membrane proteins, or penetrate the peripheral regions of the lipid bilayer. He used his own ferritin-conjugated antibody technique (Singer, 1959) and got the antibodies into the red cell ghosts by fixing the ghosts while they had holes in their membranes from incubation in hypotonic medium (Seeman, 1967). Similarly loss of unc-70, a β-spectrin ortholog in C. elegans is associated with inhibited axon outgrowth as well as spontaneous axon breaking (Hammarlund et al., 2000; Hammarlund et al., 2007). Protein 4.1 is a peripheral membrane protein that strengthens the actin- spectrin based membrane skeleton of the red blood cell and also serves to attach this structure to the plasma membrane. In addition to the structural proteins that coimmunoprecipitated with αII-spectrin (Sridharana et al., 2006), there were also proteins involved in DNA repair (e.g., XPA, XPB, XPF, ERCC1), Fanconi anemia (e.g., FANCA, FANCC, FANCD2), chromatin remodeling (e.g., actin, BRG1, hBRM, and CSB), or transcription and RNA processing (e.g., P40, hnRNP A2/B1, PML). Other nuclear proteins are known to associate with nuclear αII-spectrin, but whether they bind directly or indirectly is unknown. In contrast, proteins like spectrin belonged to a distinct category. A brain-specific β-spectrin, fodrin, relocalizes from the cortical plasma membrane to intermediate filaments upon neurite formation in PC12 cells (Takemura et al., 1993) and is transported down the axon in RGCs and SGC, possibly in a KIF3-dependent manner (Takeda et al., 2000; Willard and Simon, 1983) and localizes in the central domain of the growth cone (Sobue and Kanda, 1989). a peripheral protein that binds tightly to spectrin in the red blood cell membrane; it also binds to certain glycophorins and helps determine the shape and flexibility of the red blood cell. It was first identified in erythrocytes, where it forms a filamentous network required for red blood cells to maintain their shape and elasticity (Marchesi and Steers, 1968). For example, siRNA-downregulated lymphoblastoid cells and HeLa cells show chromosomal instability and hypersensitivity to DNA interstrand cross-linking agents (McMahon et al., 2009). A peripheral protein, called ankyrin, binds to the spectrin β subunit toward the junctional end of the heterodimers and links spectrin to the cytoplasmic NH 2-terminal domain of band 3. Peripheral Proteins: Mitochondrial cytochrome c and erythrocyte spectrin are examples of peripheral proteins. The remaining α and β products are expressed in other cell types, such as neurons and epithelia. The αI-spectrin gene is expressed in erythrocytes, whereas αII-spectrin is highly expressed in vertebrate nucleated cells (Cianci et al., 1999; Young and Kothary, 2005). Four abnormalities in RBC membrane proteins have been identified in this disorder: spectrin deficiency alone, combined spectrin and ankyrin deficiency, band 3 deficiency, and protein 4.1 defects. Spherocytic RBCs are rapidly removed from the circulation by the spleen. Copyright © 2021 Elsevier B.V. or its licensors or contributors. In 1971, “next to nothing was known about the organization of membrane proteins,” says S. Jonathan Singer (University of California, San Diego, CA). If the standard osmotic fragility test is negative, incubated osmotic fragility tests can be performed to identify more subtle cases. The lipid membrane peels off in small fragments called blebs, or vesicles and immediately reseals keeping the cytoplasmic volume intact. Spectrin deficiency is often present with other genetic mutations as alterations in their products affect the assembly of spectrin into the cytoskeleton. It is composed of two subunits, α and β spectrin, that are structurally related but functionally distinct. Meaning of spectrin. The phenotypes caused by αII-spectrin depletion support the idea that αII-spectrin functions in both the cytoskeleton and the nuclei. As a result of this lack of spectrin, erythrocytes cannot effectively maintain their biconcave structure, and assume a spherical shape. A closer-knit spectrin family of proteins shares the same general domain structure and molecular shape as human erythrocyte spectrin. We use cookies to help provide and enhance our service and tailor content and ads. Peripheral proteins also exist beneath the plasma membrane of many nucleated cells, but these proteins form a discontinuous network under the membrane, do not include spectrin, and generally allow most integral proteins to diffuse globally in the membrane (Frye and Edidin, 1970). It is now known that spectrin is the most abundant peripheral membrane protein in red blood cells and the principal component of a protein meshwork, or membrane skeleton, that underlies the cell membrane. Some researchers thought spectrin was typical of membrane proteins in general. Spectrin is a major component of the normal red blood cell (RBC) cytoskeleton and consists of two intercoiled non-identical filamentous subunits that form heterodimers. However, PSD-95 remains in spines even after filament depolymerization (Allison et al., 1998, 2000), suggesting that PSD-95 may form a stable core scaffold that does not require the cytoskeleton for its aggregation. The spectrin family of proteins includes α- and β-spectrin and α- and β-fodrin (also referred to as α- and β-spectrin II, or brain spectrin). By interacting with transmembrane proteins such as ankryin, spectrin connects the actin cytoskeleton to cell membranes (Goodman et al., 1995; Czogalla and Sikorski, 2005). Interestingly, protein 4.1 is essential to assemble nuclei in vitro in cell-free extracts of Xenopus eggs (Krauss et al., 2003). In contrast to integral membrane proteins, peripheral membrane proteins tend to collect in the water-solubl Human spectrins are encoded by seven genes, with two encoding α-spectrins (αI and αII) and five encoding β-spectrins (βI through βV) (Bennett and Baines, 2001). Ankyrin serves as the primary linkage protein for the high-affinity binding of spectrin to the inner membrane through interactions with the cytoplasmic domain of band 3. By continuing to use our website, you are agreeing to, βiv Spectrin, a New Spectrin Localized at Axon Initial Segments and Nodes of Ranvier in the Central and Peripheral Nervous System. It is now known that spectrin is the most abundant peripheral membrane protein in red blood cells and the principal component of a protein meshwork, or membrane skeleton, that underlies the cell membrane. The αII-spectrin deficiency phenotype in WM-266 human melanoma cells included loss of stress fibers, cell adhesion defects, and reduced density of focal adhesions, as well as reduced proliferation with cell cycle arrest at the G1 phase, Rb phosphorylation, and elevated expression of the cyclin-dependent kinase inhibitor, p21Cip (Metral et al., 2009). - spectrin; a and b chains, most abundant important for maintainence of rbc membrane shape as it binds to other peripheral proteins to form cytoskeletal network of microfilaments on inner membrane surface controls biconcave shape and deformity of the cell - ankyrin; anchors lipid bilayer to cytoskeleton via association with band 3 and spectrin A peripheral smear from these patients will demonstrate spherocytes with polychromasia (increased reticulocytes).