Transient intercellular adhesion: the importance of weak protein-protein interactions (original) (raw)
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Cell adhesion. Competition between nonspecific repulsion and specific bonding
Biophysical Journal, 1984
We develop a thermodynamic calculus for the modeling of cell adhesion. By means of this approach, we are able to compute the end results of competition between the formation of specific macromolecular bridges and nonspecific repulsion arising from electrostatic forces and osmotic (steric stabilization) forces. Using this calculus also allows us to derive in a straightforward manner the effects of cell deformability, the Young's modulus for stretching of bridges, diffusional mobility of receptors, heterogeneity of receptors, variation in receptor number, and the strength of receptor-receptor binding. The major insight that results from our analysis concerns the existence and characteristics of two phase transitions corresponding, respectively, to the onset of stable cell adhesion and to the onset of maximum cell-cell or cell-substrate contact. We are also able to make detailed predictions of the equilibrium contact area, equilibrium number of bridges, and the cell-cell or cell-substrate separation distance. We illustrate how our approach can be used to improve the analysis of experimental data, by means of two concrete examples.
Journal of Biological Chemistry, 2004
The mechanism by which the neural cell adhesion molecule, N-CAM, mediates homophilic interactions between cells has been variously attributed to an isologous interaction of the third immunoglobulin (Ig) domain, to reciprocal binding of the two N-terminal Ig domains, or to reciprocal interactions of all five Ig domains. Here, we have used a panel of recombinant proteins in a bead-binding assay, as well as transfected and primary cells, to clarify the molecular mechanism of N-CAM homophilic binding. The entire extracellular region of N-CAM mediated bead aggregation in a concentration-and temperature-dependent manner. Interactions of the Nterminal Ig domains, Ig1 and Ig2, were essential for bead binding, based on deletion and mutation experiments and on antibody inhibition studies. These findings were largely in accord with aggregation experiments using transfected L cells or primary chick brain cells. Additionally, maximal binding was dependent on the integrity of the intramolecular domain-domain interactions throughout the extracellular region. We propose that these interactions maintain the relative orientation of each domain in an optimal configuration for binding. Our results suggest that the role of Ig3 in homophilic binding is largely structural. Several Ig3 specific reagents failed to affect N-CAM binding on beads or on cells, while an inhibitory effect of an Ig3 specific monoclonal antibody is probably due to perturbations at the Ig2-Ig3 boundary. Thus, it appears reciprocal interactions between Ig1 and Ig2 are necessary and sufficient for N-CAM homophilic binding, but that maximal binding requires the quaternary structure of the extracellular region defined by intramolecular domain-domain interactions. 2 by guest on May 4, 2017 http://www.jbc.org/ Downloaded from The factors affecting interactions of molecules on the cell surface including adhesion molecules are more complex than for comparable solution interactions. Molecules bound to the cell membrane experience restricted motion, and thus factors including molecular size and flexibility may be important determinants of binding strength or adhesiveness (1). In addition, the orientation of molecules on the cell surface may influence the presentation of binding sites and thereby affect recognition by an apposing cell (2). Furthermore, robust cell-cell binding requires multiple adhesive interactions, as the binding affinities determined for adhesion molecules in solution are weak (3, 4). Solution and crystallographic studies of cell adhesion molecules have revealed details of their domain structures and identified potential adhesive intermolecular interactions. However, such studies can not readily assess the influences of the specific factors associated with cell-cell interactions on binding affinities. Alternative approaches developed for studying the interactions of molecules bound to surfaces including studies in hydrodynamic flow chambers, and surface force and atomic force microscopy are providing quantitative information of the interactions of molecules on a cell membrane (5, 6, 7).
The Structural Analysis of Adhesions Mediated by Ep-CAM
Experimental Cell Research, 1999
The epithelial cell adhesion molecule Ep-CAM is capable of mediating Ca2+-independent homotypic cell-cell adhesion when introduced into cells lacking their own means of cell-cell interactions. We used (confocal) immunofluorescent and (immuno-) electron microscopy to investigate the structural organization of Ep-CAM-mediated adhesions and their relation to other types of intercellular adhesions. Ep-CAM-transfected cell lines, cells of epithelial origin, and epithelial tissues were analyzed. In transfected L cells Ep-CAM brings the opposing intercellular membranes into a close proximity (approximately 10-14 nm) at sporadic contacts; however, no structures resembling junctional complexes were observed. In L cells cotransfected with Ep-CAM and E-cadherin, both molecules localize at the sites of cell-cell contact, forming independent adhesion sites with no Ep-CAM detectable within the structurally distinguishable cadherin-mediated adherens junctions. In well-differentiated carcinoma cell lines Ep-CAM colocalized with E-cadherin practically along the whole lateral domain; however, no colocalization was observed between Ep-CAM and the components of the tight junction complex (occludin and ZO-1), desmosomes (desmoplakins I/II), or cell-substrate adhesions (beta1 integrins). This was confirmed by analysis of polarized epithelium of normal colon where Ep-CAM was present at the lateral membrane including the adherens junction areas, but was fully excluded from the apical cell membrane (microvilli), tight junctions, and desmosomes. We conclude that (1) Ep-CAM does not form junctional complexes in L cells, (2) in epithelial cells, cell surface Ep-CAM is present at the lateral cell membrane, but is excluded from tight junctions and desmosomes, and (3) in epithelial cells, Ep-CAM is present within adhesions mediated by the classic cadherins (especially E-cadherin) with both types of molecules remaining as independent clusters. The colocalization with cadherins might be important for the modulating effect of Ep-CAM on cadherin-mediated adhesions.
Studies on intercellular adhesion. Induction of adhesion by multivalent ligands
Journal of Biological Chemistry
Multivalent ligands capable of binding to cells facilitate intercellular adhesion by bridging adjoining cells. This process serves as an indirect means of promoting adhesion merely by holding the cells in close proximity. The present paper demonstrates that a different, more specific type of adhesion enhancement results when the cells are induced to adhere by cross-linking specific cell surface receptors.
Biological cells adhesion mediated by receptors–ligands binding
2014
Cell adhesion plays a vital role in many cell activities. The motivation to model cell adhesion is to study important biological processes, such as cell spreading, cell aggregation, tissue formation, and cell adhesion to biomaterials. This study provides important insight into cell adhesion, which can lead to improve regenerative medicine and tissue formation techniques. In this study, we focus on modeling the adhesion of biological cells mediated by receptors-ligands binding and the diffusivity of the receptor on the cell membrane surface. The ability of receptors to diffuse on the cell membrane surface yields a very unique and complicated adhesion mechanism, which is excusive to cell membrane. The biological cell is modeled as a fl uid-like membrane with negligible bending stiffness enclosing a cytoplasm fl uid. The mobility of the receptor on the cell membrane is modeled using the diffusion equation. The phospholipid bilayer, which is the main component in the cell membrane, shows fl uid-like behavior associated with the molecules' diffusivity. The in-plane mechanical behavior of the cell membrane is assumed to depend only on the area change, which is motivated by the fl uidity of the phospholipid bilayer. In addition, the presence of receptors infl uences the local mechanical properties of the cell membrane. The infl uence of the receptor density is accounted for by including stress-free area change, which depends on the receptor density. Based on the physical properties of the receptors and ligands we modeled the attraction between the receptors and ligands as a charged-nonpolar which is a noncovalent interaction. Such interaction is a short-range type, which decays fast with distance. Fick's law is used to model the receptor-receptor interactions. The resultant interaction force, which includes receptor-ligand and receptor-receptor interaction, is decomposed into tangential part, which governs the receptor diffusion, and normal part, which governs the cell deformation and adhesion. The formulation of the governing equations and numerical simulations will be presented.
Minimal Encounter Time and Separation Determine Ligand-Receptor Binding in Cell Adhesion
Biophysical Journal, 2011
The binding properties of biomolecules play a crucial role in many biological phenomena, specially cell adhesion. While the attachment kinetics of soluble proteins is considered as well known, complex behavior arises when protein molecules are bound to the cell membrane. We probe the hidden kinetics of ligand-receptor bond formation using single molecule flow chamber assays and brownian dynamics simulations. We show that, consistent with our recently proposed hypothesis, association requires a minimum duration of contact between the reactive species. In our experiments, ICAM-1 anchored on a flat substrate bind to anti-ICAM-1 coated on flowing microbeads. The interaction potential between bead and substrate is measured by micro-interferometry and is used as an ingredient to simulate bead movement. Our simulation calculates the duration of ligand-receptor contacts imposed by the bead movement. We quantitatively predict the reduction of adhesion probability measured for shorter tether length of the ligand or if a repulsive hyaluronan layer is added on the surface. To account for our results, we propose that bond formation may occur in our system by crossing of a diffusive plateau in the energy landscape, on the timescale of 5 ms and an energy barrier of 5 k B T , before reaching the first detectable bound state. Our results show how to relate cell scale behavior to the combined information of molecular reactivity and biomolecules submicron scale environment.
Evidence for regulated dimerization of cell-cell adhesion molecule (C-CAM) in epithelial cells
The Biochemical journal, 1996
C-CAM is a Ca(2+)-independent cell adhesion molecule (CAM) belonging to the immunoglobulin superfamily. Addition of chemical cross-linkers to isolated rat liver plasma membranes, intact epithelial cells and purified preparations of C-CAM stabilized one major C-CAM-containing product whose apparent molecular mass was approximately twice that of the C-CAM monomer. The failure to detect additional proteins after cleavage of the cross-linked species demonstrated that C-CAM exists as non-covalently linked dimers both in solution and on the cell surface. Dimerization occurred to the same extent in adherent monolayers and in single cell populations, indicating that dimer formation was the result of cis-interactions within the membranes of individual cells. Using isoform-specific anti-peptide antibodies, both C-CAM1 and C-CAM2 were found to be involved in dimerization, forming predominantly homo-dimeric species. Both calmodulin and Ca2+ ionophore modulated the level of dimer formation, sugg...
The Measurement of Intercellular Adhesion
Proceedings of The National Academy of Sciences, 1967
Differential intercellular adhesions may play an important role in morphogenetic phenomena. To analyze this role, however, a technique is needed with which differential adhesion between cells may be unambiguously detected and measured.
European Biophysics Journal, 1997
CD2 is a cell adhesion molecule found on the plasma membrane of T-lymphocytes. Its counter-receptor in rat is the structurally related CD48. This interaction is believed to contribute to the adhesion of T-cells to other cells such as cytotoxic targets and antigen presenting cells. Cell-cell adhesion involves the formation of multiple cell adhesion molecule complexes at the cell surface and if cellcell de-adhesion is to occur, these complexes need to be disrupted. The affinities of cell adhesion molecule interactions are suggested to be relatively weak to allow this de-adhesion of cell-cell interactions. The CD2/CD48 interaction has been studied using recombinant extracellular proteins and the affinity of the interaction of soluble recombinant rat CD2 -CD48 has been determined (at 37°C) using surface plasmon resonance (and shown to be weak), with the dissociation constant K d = 60 -90 µM. The values determined by surface plasmon resonance results could be affected by the immobilisation of the ligand on the chip and any self-association on the chip. We used three different analytical ultracentrifuge procedures which each allowed the interaction to be studied in free solution without the need for an immobilisation medium. Both sedimentation equilibrium (using direct analysis of the concentration distribution and also modelling of molecular weight versus concentration data) and sedimentation velocity at 5°C yielded dissociation constants in the range of 20 -110 µM, supporting the surface plasmon resonance findings showing that binding between these cell adhesion molecules is relatively weak. These studies also ruled out the presence of any significant self-association of the reactants which could lead to systematic error in the surface plasmon resonance results.