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A simple method for displaying the hydropathic character of a protein

Electrophoretic analysis of the major polypeptides of the human erythrocyte membrane.

A fluid mosaic model is presented for the gross organization and structure of the proteins and lipids of biological membranes. The model is consistent with the restrictions imposed by thermodynamics. In this model, the proteins that are integral to the membrane are a heterogeneous set of globular molecules, each arranged in an amphipathic structure, that is, with the ionic and highly polar groups protruding from the membrane into the aqueous phase, and the nonpolar groups largely buried in the hydrophobic interior of the membrane. These globular molecules are partially embedded in a matrix of phospholipid. The bulk of the phospholipid is organized as a discontinuous, fluid bilayer, although a small fraction of the lipid may interact specifically with the membrane proteins. The fluid mosaic structure is therefore formally analogous to a two-dimensional oriented solution of integral proteins (or lipoproteins) in the viscous phospholipid bilayer solvent. Recent experiments with a wide variety of techniqes and several different membrane systems are described, all of which abet consistent with, and add much detail to, the fluid mosaic model. It therefore seems appropriate to suggest possible mechanisms for various membrane functions and membrane-mediated phenomena in the light of the model. As examples, experimentally testable mechanisms are suggested for cell surface changes in malignant transformation, and for cooperative effects exhibited in the interactions of membranes with some specific ligands. Note added in proof: Since this article was written, we have obtained electron microscopic evidence (69) that the concanavalin A binding sites on the membranes of SV40 virus-transformed mouse fibroblasts (3T3 cells) are more clustered than the sites on the membranes of normal cells, as predicted by the hypothesis represented in Fig. 7B. T-here has also appeared a study by Taylor et al. (70) showing the remarkable effects produced on lymphocytes by the addition of antibodies directed to their surface immunoglobulin molecules. The antibodies induce a redistribution and pinocytosis of these surface immunoglobulins, so that within about 30 minutes at 37 degrees C the surface immunoglobulins are completely swept out of the membrane. These effects do not occur, however, if the bivalent antibodies are replaced by their univalent Fab fragments or if the antibody experiments are carried out at 0 degrees C instead of 37 degrees C. These and related results strongly indicate that the bivalent antibodies produce an aggregation of the surface immunoglobulin molecules in the plane of the membrane, which can occur only if the immunoglobulin molecules are free to diffuse in the membrane. This aggregation then appears to trigger off the pinocytosis of the membrane components by some unknown mechanism. Such membrane transformations may be of crucial importance in the induction of an antibody response to an antigen, as well as iv other processes of cell differentiation.

The fluid mosaic model of the structure of cell membranes.

Signaling Recognition Events with Fluorescent Sensors and Switches.

Throughout the biological world, a 30 A hydrophobic film typically delimits the environments that serve as the margin between life and death for individual cells. Biochemical and biophysical findings have provided a detailed model of the composition and structure of membranes, which includes levels of dynamic organization both across the lipid bilayer (lipid asymmetry) and in the lateral dimension (lipid domains) of membranes. How do cells apply anabolic and catabolic enzymes, translocases and transporters, plus the intrinsic physical phase behaviour of lipids and their interactions with membrane proteins, to create the unique compositions and multiple functionalities of their individual membranes?

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Membrane lipids: where they are and how they behave.

The elucidation of the molecular architecture of cell membranes is a central goal for cell biology, as structure lies at the heart of function. The erythrocyte plasma membrane has long provided a favored testing ground for this inquiry. Human red blood cells are readily available, relatively homogeneous, and relevant to medicine. Their plasma membranes can be easily isolated intact and essentially free of contamination from other cells, organelles, and cytoplasmic contents. This membrane is complex enough to be interesting and, to some degree, representative, yet it is simple enough to be analyzed as a whole. These circumstances make it likely that the human red cell plasma membrane will be the first whose molecular anatomy is known in any degree of satisfying detail. The literature concerning the proteins of erythrocyte membranes and membranes in general has been the subject of repeated review (1 9). This article will focus on the localization and modes of association of individual major polypeptides within the human red cell membrane.

https://rupress.org/jcb/article-pdf/62/1/1/1386885/1.pdf

THE ORGANIZATION OF PROTEINS IN THE HUMAN RED BLOOD CELL MEMBRANE A Review

Preparation of impermeable ghosts and inside-out vesicles from human erythrocyte membranes.

Treatment of isolated human erythrocyte membranes with Triton X-100 at ionic strength ⋍0.04 preferentially released all the glycerolipid and glycoprotein species. At low ionic strength, certain nonglycosylated polypeptides were also selectively solubilized. The liberated polypeptides were free of lipids, but some behaved as if associated into specific oligomeric complexes. Each detergent-insoluble ghost residue appeared by electron microscopy to be a filamentous reticulum with adherent lipoid sheets and vesicles. The residues contained most of the membrane sphingolipids and the nonglycosylated proteins. The polypeptide elution profile obtained with nonionic detergents is therefore nearly reciprocal to that previously seen with a variety of agents which perturb proteins. These data afford further evidence that the externally-oriented glycoproteins penetrate the membrane core where they are anchored hydrophobically, whereas the nonglycosylated polypeptides are, in general, bound by polar associations at the inner membrane surface. The filamentous meshwork of inner surface polypeptides may constitute a discrete, self-associated continuum which provides rather than derives structural support from the membrance.

Selective solubilization of proteins and phospholipids from red blood cell membranes by nonionic detergents

Isolated human erythrocyte membranes were exposed to a series of reagents known to modify or perturb proteins; these included sodium hydroxide, lithium diiodosalicylate, acid anhydrides, and organic mercurials. Each reagent liberated the same set of relatively polar polypeptides from the membrane, while the other, more hydrophobic species invariably remained associated with the membrane residue. The selective elution pattern was precisely that seen previously with 6 M guanidine hydrocloride. The released polypeptides, comprising half of the membrane protein mass, contained no carbohydrate; current evidence indicates that all of these components are confined to the cytoplasmic surface of the membrane. The residue contained all the lipids and all the glycoproteins. The latter are accessible to the outer membrane surface and, in at least two cases, seem to extend asymmetrically across the thickness of the membrane. Thus, the distinctive elution behavior which defines these two groups of polypeptides relates both to their chemical composition and their organizational disposition in the membrane.

Theodore L. Steck

Papers

Electrophoretic analysis of the major polypeptides of the human erythrocyte membrane.

THE ORGANIZATION OF PROTEINS IN THE HUMAN RED BLOOD CELL MEMBRANE A Review

Preparation of impermeable ghosts and inside-out vesicles from human erythrocyte membranes.

Selective solubilization of proteins and phospholipids from red blood cell membranes by nonionic detergents

Selective solubilization of proteins from red blood cell membranes by protein perturbants.