Clustering Of Cell Surface Receptors Research Articles

Local accumulation of alpha-spectrin-related protein under plasma membrane during capping and phagocytosis in Acanthamoeba.

During capping and phagocytosis the interaction between cluster cell surface receptors and the submembraneous actin-based skeleton may be mediated by spectrin-like proteins. To test this possibility we examined the localization of an alpha-spectrin immunoanalogue, that had been previously identified in whole extracts of Acanthamoeba, during capping of Con A receptors and during phagocytosis of Con A-coated yeast. During capping alpha-spectrin and filamentous actin co-migrated with the Con A receptors and accumulated in the region of cap formation, as demonstrated by double immunofluorescence studies. Immunoelectron microscopy revealed submembraneous location of alpha-spectrin in cells exposed to Con A, both at the time of initial cross-linking and during accumulation of alpha-spectrin in the region of the cap. Phagocytosis studies showed that alpha-spectrin and actin filaments were concentrated around phagocytic cups that enclosed ConA-coated yeast upon internalization. The proteins also surrounded nascent phagosomes present in the vicinity of the plasma membrane but were absent at the later time point of phagosome maturation. These data demonstrate a correlation between clustering of cell surface receptors and submembraneous localization of alpha-spectrin, suggesting an involvement of spectrin-like proteins in mediating the interaction of receptor clusters with the actin cytoskeleton.

Dynamics of a Thin Liquid Film with a Surface Chemical Reaction

The detailed description of the influence of a chemical reaction on the dynamic behavior of a thin liquid film is of significant importance in many engineering and biological applications. In this paper, the dynamics of a thin liquid film on a solid substrate is followed until film rupture or formation of local contacts. A surface chemical reaction between insoluble surfactant molecules (receptors) on the free surface of the film and binding sites on the solid substrate is considered. Asymptotic expansion of the equations for fluid motion with van der Waals, capillary, and Marangoni forces leads to a model with three nonlinear evolution equations describing the dynamics of the surface deformation and the kinetics of free and bound receptors. Chemical and hydrodynamic modes are predicted and simulated numerically with different stability regimes: for a simple linear surface reaction, the concentration of receptors follows the deformation of the surface; for a nonlinear surface reaction with affinity enhanced at small distances, a clustering of receptors is observed at the local points of contact. A completely new regime is also obtained where the rupture (or contact) time is delayed by several orders of magnitude, and the concentrations and film thickness may oscillate. This study could be relevant to biological applications where adhesion between cells and substrates can be modeled by considering the dynamics of the thin film between them. The results are first compared with experiments on biological cells adhering to glass or other solid substrates where periodic patterns (wavelike morphologies) are observed with a clustering of adhesion receptors at the local contact points. A second possible application is the activation of T lymphocytes, a major immunological cell type, which requires the clustering of cell surface receptors by interaction of T-cell receptors with surface-bound ligands.

High-order fluorescence fluctuation analysis of model protein clusters.

The technique of high-order fluorescence fluctuation autocorrelation for detecting and characterizing protein oligomers was applied to solutions containing two fluorescent proteins in which the more fluorescent proteins were analogues for clusters of the less fluorescent ones. The results show that the model protein clusters can be detected for average numbers of observed subunits (free monomers plus monomers in oligomers) equal to 10-100 and for relative fluorescent yields that correspond to oligomers as small as trimers. High-order fluorescent fluctuation analysis may therefore be applicable to cell surface receptor clusters in natural or model membranes.

Fluorescence correlation spectroscopy for detecting submicroscopic clusters of fluorescent molecules in membranes

The formation of cell surface receptor clusters has been implicated of confirmed in the mechanism of signal transduction across biological membranes for a variety of processes, including receptor-mediated phagocytosis and endocytosis and cellular response to hormones and neurotransmitters. Flourescence correlation spectroscopy (FCS) is one technique that may provide insight into the kinetics and extent of receptor aggregation. Recent theoretical and experimental developments in FCS for the investigation of submicroscopic clusters of fluorescence molecules are described and the potential applications of the technique to receptor aggregation are reviewed.

Theory of clustering of cell surface receptors by ligands of arbitrary valence: dependence of dose response patterns on a coarse cluster characteristic

The interaction of ligands with cell surface receptors often induces the formation of receptor clusters on the plasma membrane. This paper develops methods for calculating the kinetics of clustering of divalent receptors by ligands of arbitrary valence. Intramolecular bonding (i.e., both sites on the same receptor bound to a single ligand) is explicitly included in the formalism. The equations are necessary for, among other things, a quantitative analysis of the response of basophils and mast cells to multivalent haptens and antigens. The implications of the equations are briefly pursued. Among the results are: (1) The presence of intramolecular reaction has two opposing effects on the concentration of cross-links, increasing them at low ligand concentrations and suppressing them at high ligand concentrations. The result suggests that those bivalent haptens which do not induce a response may, nevertheless, be active when they are in the form of higher valence analogues. (2) The relation K= 1 2c ∗ between the ligand concentration at which histamine release peaks ( c ∗), and the ligand site-receptor site affinity ( K), which holds for symmetric bivalent haptens, has no simple exact analogue for multivalent ligand. A good approximate relation that holds when K ″ 2> Kc ∗ is KK ″= 1 ƒc ∗ , where K ″ 2 is the intramolecul equilibrium constant at very low ligand concentrations, and f(⩾2) is the valence of the ligand. (3) The dose dependence of a response that is proportional to concentration of cross-links is qualitatively different from one that is proportional to the concentration of aggregates. In particular, the concentration of aggregates may be a bimodal function of ligand concentration. The deviations from simple unimodal dose-response patterns that are sometimes observed in histamine release experiments may, therefore, in part reflect the cell's inability to discriminate between cluster sizes beyond a certain small size. (4) The dose dependence of the number of aggregates per cell shows a switch from unimodal to bimodal as valence is increased. (5) The bimodal pattern is markedly asymmetric, with a high concentration peak that is considerably larger than the low concentration peak. (6) For conditions under which such bimodality is obtained, the addition of monomer will decrease the number of aggregates at very low concentrations, but increase the number over the limb that descends from the low concentration mode. For low affinity ligands ( K=10 4 M –1), the low concentration mode will be the only one observed. Hence a response that is a function of the number of aggregates will sometimes be observed to increase at supraoptimal concentrations when monomer is added. (7) The number of aggregates induced by bivalent ligands can, for certain limited but relevant concentration and parameter ranges, exceed the number induced by higher valence analogues. The predictions are discussed in terms of available experimental data.

Receptor clustering on a cell surface. II. theory of receptor cross-linking by ligands bearing two chemically distinct functional groups

The clustering of cell surface receptors by interaction with extracellular multivalent ligands has been shown to be an important event in triggering cellular responses in a number of cells, the release of histamine by mast cells and basophils being a prime example. Here I develop and analyze a model for the binding of a bivalent ligand, containing two different functional groups, to a cell which has distinct receptors on its surface for these groups. Because each ligand is capable of binding two receptors, initial binding of the ligand to a receptor site is followed by cross-linking reactions on the surface that lead to the formation of ligand-receptor clusters. Both equilibrium and kinetic aspects of this ligand binding and receptor cross-linking problem are studied. In the presence of monovalent hapten, receptor sites are occupied and become unavailable for cross-linking. A quantitative treatment of this inhibitory effect is also presented.