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Biophysical Journal 85:646-655 (2003)
© 2003 The Biophysical Society

Functional Incorporation of Integrins into Solid Supported Membranes on Ultrathin Films of Cellulose: Impact on Adhesion

Stefanie Goennenwein *, Motomu Tanaka *, Bin Hu {dagger}, Luis Moroder {ddagger} and Erich Sackmann *

* Technische Universität München, Garching, Germany; {dagger} Lerner Research Institute, The Cleveland Clinic Foundation, Cleveland, Ohio 44195; USA; and {ddagger} Max Planck Institut für Biochemie, Martinsried, Germany

Correspondence: Address reprint requests to Stefanie Goennenwein, Technische Universität München, James-Franck-Str. 1, D-85748 Garching, Germany. Tel.: 49-8928912470; Fax: 49-8928912469; E-mail: smarx{at}ph.tum.de.

Biomimetic models of cell surfaces were designed to study the physical basis of cell adhesion. Vesicles bearing reconstituted blood platelet integrin receptors {alpha}IIbß3 were spread on ultrathin films of cellulose, forming continuous supported membranes. One fraction of the integrin receptors, which were facing their extracellular domain toward the aqueous phase, were mobile, exhibiting a diffusion constant of 0.6 µm2 s-1. The functionality of receptors on bare glass and on cellulose cushions was compared by measuring adhesion strength to giant vesicles. The vesicles contained lipid-coupled cyclic hexapeptides that are specifically recognized by integrin {alpha}IIbß3. To mimic the steric repulsion forces of the cell glycocalix, lipids with polyethylene glycol headgroups were incorporated into the vesicles. The free adhesion energy per unit area {Delta}gad was determined by micro-interferometric analysis of the vesicle's contour near the membrane surface in terms of the equilibrium of the elastic forces. By accounting for the reduction of the adhesion strength by the repellers and from measuring the density of receptors one could estimate the specific receptor ligand binding energy. We estimate the receptor-ligand binding energy to be 10 kBT under bioanalogue conditions.




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