Membrane skeleton proteins

Red Blood Cell Membrane and Membrane Skeleton Proteins... 

Peripheral membrane proteins can readily be removed by changes in ionic strength or pH. Extraction of the membrane ghosts with detergent removes integral membrane proteins that are not part of the membrane skeleton and leaves behind only the membrane skeleton proteins. The proteins of the intact ghost and membrane skeleton only are shown in Figure 10.17. 

Fehon R.G., Dawson I.A., and Artavanis-Tsakonas S. 1994. A Drosophila homologue of membrane-skeleton protein 4.1 is associated with septate junctions and is encoded by the coracle gene. Development 120 545-557. 

Mechanical functions of cells require interactions between integral membrane proteins and the cyto-skeleton. These functions include organization of signaling cascades, formation of cell junctions and regulation of cell shape, motility, endo- and exocytosis. Several different families of membrane-associated proteins mediate specific interactions among integral membrane proteins, cytoskeletal proteins and contractile proteins. Many of these linker proteins consist largely of various combinations of conserved protein-association domains, which often occur in multiple variant copies. 

Beck, K. A. and Nelson, I. The spectrin-based membrane skeleton as a membrane protein-sorting machine. Am.. Physiol. 270 C1263-C1270,1996. 

What is the function of the membrane skeleton There is a group of hereditary diseases including spherocytosis in which erythrocytes do not maintain their biconcave disc shape but become spherical or have other abnormal shapes and are extremely fragile.269 272 Causes of spherocytosis include defective formation of spectrin tetramers and defective association of spectrin with ankyrin or the band 4.1 protein.265 273 Thus, the principal functions of these proteins in erythrocytes may be to strengthen the membrane and to preserve the characteristic shape of erythrocytes during their 120-day lifetime in the bloodstream. In other cells the spectrins are able to interact with microtubules, which are absent from erythrocytes, and to microtubule-associated proteins of the cytoskeleton (Chapter 7, Section F).270 In nerve terminals a protein similar to erythrocyte protein 4.1 may be involved in transmitter release.274 The cytoskeleton is also actively involved in transmembrane signaling. 

Related proteins occur in other tissues.488 The 911-residue band 3 protein consists of two distinct parts of nearly equal size. The N-terminal portion is attached to the membrane skeleton (Fig. 8-16). The C-terminal part, which is embedded in the membrane, is thought to form 14 transmembrane helices and to contain the ion exchange channel or channels.4893 As previously mentioned, defects in the N-terminal portion cause spherocytosis. The mutation Arg 589 His in the C-terminal half causes renal tubular acidosis in which the kidneys do not adequately remove acids from the body.238 489 Band 3 proteins can also exchange phosphate, sulfate, and phosphoenolpyruvate for Cl or bicarbonate. 

The structure of spectrin and the location of spectrin in the cytoskeleton. (a) An a/3 dimer of spectrin. Both a and f3 subunits are extended structures consisting of end-to-end domains of 106 amino-acyl residues folded into three a helices the subunits twist about one another loosely as shown. (b) The erythrocyte membrane skeleton. Spectrin tetramers ((X2P2), shown in yellow, are linked to the cytoplasmic domain of the anion channel (blue) by the protein ankyrin (red), and to glycophorin and actin filaments by protein 4.1. This structure lends stability to the red cell membrane while maintaining sufficient flexibility to allow erythrocytes to withstand substantial shear forces in the peripheral circulation. 

The membrane skeleton acts as an elastic semisolid, allowing brief periods of deformation followed by reestablishment of the original cell shape (reviewed by Bennett and Gilligan, 1993). Erythrocytes in the human bloodstream have to squeeze repeatedly through narrow capillaries of diameters smaller than their own dimensions while resisting rupture. A functional erythrocyte membrane is pivotal to maintaining the functional properties of the erythrocyte. This importance is apparent when examination is made of many hemolytic anemias, where mutation of proteins involved in the structure of the submembranous cytoskeleton, and its attachment to the lipid bilayer, result in a malformed or altered cytoskeletal architecture and a disease phenotype. 

The primary biochemical defects of HS are linked to proteins important to the interaction between the membrane skeleton and the lipid bilayer involving a- and /3-spectrin, ankyrin, band 3, and protein 4.2 (Gallagher and Forget, 1998). Combined spectrin and ankyrin deficiency (Coetzer et al, 1988 Pekrun et al, 1993 Sawides et al., 1993) is most commonly observed, followed by band 3 deficiency (Iolascon et al, 1992 Jarolim et al,... 

Earnest, J. P., Santos, G. F., Zuerbig, S., and Fox, J. E. (1995). Dystrophin-related protein in the platelet membrane skeleton. Integrin-induced change in detergent-insolubility and cleavage by calpain in aggregating platelets. J. Biol. Chem. 270, 27259-27265. 

Jarolim, P., Lahav, M., Liu, S. C., and Palek, J. (1990). Effect of hemoglobin oxidation products on the stability of red cell membrane skeletons and the associations of skeletal proteins Correlation with a release of hemin. Blood 76, 2125-2131. 

The major components of the membrane skeleton are spectrin, actin, and protein 4.1. Spectrin is a highly flexible, rodlike molecule composed of two nonidentical polypeptides a-spectrin and (3-spectrin.These chains are aligned side by side in the form of a a(3-heterodimer, and spectrin heterodimers in turn join head to head to form (aP)2-tetramers. The tail ends of spec-... 

Band 4.1 Protein 4.1 80 K P Membrane skeleton association with GPC... 

The breakdown or disorganization of the membrane skeleton can be followed by the release of some membrane-bound enzymes, such as AChE [43] or amyloid precursor protein (APP), which are crucial for the pathologic changes in the brains of AD patients. AlFx might affect the structure and function of cytoskeletal proteins by several routes [68]. It can activate various G-proteins and protein kinases, act as the analogue of GTP in the assembly-disassembly cycle, and affect the binding of cytoskeletal proteins to... 

The majority of this matrix is composed of a protein called spectrin, a heterodimeric protein containing a 220-kDa a subunit and a similar but slightly larger /3 subunit. The highly repetitive amino acid sequences of both the a and /3 subunits give them a filamentous three-dimensional structure. As the a and /3 subunits of spectrin associate with one another, they form the flexible monomeric units that are used to create the membrane skeleton. 

Tvo additional peripheral membrane proteins anchor the spectrin filaments to the cytoplasmic side of the erythrocyte membrane. One of these polypeptides, the 210-kDa ankyrin protein, binds both a single spectrin molecule and the chloride-bicarbonate anion-exchange protein discussed previously. The second of these polypeptides, actin, is capable of binding several molecules of spectrin. Since actin is able to associate with more than a single spectrin monomer, it acts as a branch point for the spectrin protein as the membrane skeleton or matrix is assembled (see Fig. 13-1). In this experiment, you will determine the concentration of total protein in the erythrocyte membrane through the use of the Folin-Ciocalteau assay. 

Membrane-Skeleton Fence Model Ik Transmembrane protein... 

To reconcile this apparent contradiction the membrane skeleton fence and anchored transmembrane picket model was proposed (54). According to this model, transmembrane proteins anchored to and lined up along the membrane skeleton (fence) effectively act as a row of posts for the fence against the free diffusion of lipids (Fig. 11). This model is consistent with the observation that the hop rate of transmembrane proteins increases after the partial removal of the cytoplasmic domain of transmembrane proteins, but it is not affected by the removal of the major fraction of the extracellular domains of transmembrane proteins or extracellular matrix. Within the compartment borders, membrane molecules undergo simple Brownian diffusion. In a sense, the Singer-Nicolson model is adequate for dimensions of about 10 x lOnm, the special scale of the original cartoon depicted by the authors in 1972. However, beyond such distances simple extensions of the fluid mosaic model fail and a substantial paradigm shift is required from a two-dimensional continuum fluid to the compartmentalized fluid. 

Schematic representations of sodium dodecyl sulfate polyacrylamide gel electrophoretic patterns of red blood cell membranes (M) and membrane skeletons (S), based on work by Fairbanks and Steck. Proteins are stained with Coomassie blue (CB) and sialoglycoproteins with periodic acid-Schiff (PAS). GPA, GPB, and GPC are glycophorin A. B, and C, respectively G3PD is glyceraldehyde-3-phosphate dehydrogenase. (GPA)2 and (GPB)2 are dimers, and GPA-GPB is a heterodiraer. [Reproduced with permission from J. B. Stanbury, J. B. Wyngaarden, D. S. Fredrickson, et al. (Eds.), The Metabolic Basis of Inherited Disease, 5th ed. McGraw-Hill, New York, 1983.]...

The intricate interactions of the spectrin-protein 4.1-actin complex may be of central importance in maintaining the structural integrity of the red cell membrane. Two genetic disorders affecting the red cell membrane skeleton are hereditary spherocytosis and hereditary elliptocytosis. The former, the most common congenital form of hemolytic anemia in persons of northern European descent, exhibits an autosomal dominant inheritance pattern. The red blood cells are spherical, osmotically fragile, and considerably reduced in life span. They undergo... 

A central role of the membrane skeleton in the desensitization of FPR in human neutrophils has been well documented in recent years (for review see [5,48]). However, the nature of the molecular link of the receptor to the membrane skeleton remained elusive. The release of FPR from membrane skeletal pellets with agents that depolymerize actin [44] suggests that F-actin may participate in the immobilization process that prevents the receptor from interaction with G proteins. Although it is difficult to demonstrate a specific interaction of a receptor with a protein as abundant as actin there are a series of observations that suggest a specific and direct interaction of FPR with actin. 

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