Antagonist induced deadhesion of specifically adhered vesicles
Ana-Suncana Smith 1, Barbara G. Lorz 2, Udo Seifert 3 and Erich Sackmann 1*
1 Technical University Munich
2 E22 Institut für Biophysik, Tecnische Universität München, D-85748, Garching, Germany
3 II. Institut für Theoretische Physik, Universität Stuttgart, D-70550 Stuttgart, Germany
* To whom correspondence should be addressed. E-mail: sackmann{at}ph.tum.de.
Submitted on March 16, 2005
Revised on April 19, 2005
Accepted on 28 September 2005
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Abstract |
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By use of a model system consisting of giant vesicles adhering to flat substrates, we identified, both experimentally and theoretically, two new control mechanisms for antagonist-induced deadhesion. Adhesion is established by specific binding of surface-grafted E-selectin and vesicle-carrying oligosaccharide LewisX. Deadhesion is achieved by controlled titration of monoclonal antibodies against E-selectin. The first mechanism is characterized by a considerable retraction of the contact zone resulting in a loss of contact area between the vesicle and the substrate. Within the developed theoretical framework, the observed equilibrium state is understood as a balance between the spreading pressure of the vesicle and the antagonist-induced lateral pressure at the edge of the contact zone. In the second mechanism, the antibodies induce unbinding by penetrating the contact zone without significantly affecting its size. This process reveals the decomposition of the adhesion zone into micro-domains of tight binding separated by strongly fluctuating sections of the membrane. Both, experiment and theory show a sigmoidal decrease of the number of bound ligands as a function of the logarithm of antagonist concentration. The work presented herein also provides a new method for the determination of the receptor binding affinity of either the surface-embedded ligands or the competing antagonist molecules.
Key Words:
competitive binding of antibodies, lateral osmotic pressure, reflection interference contrast microscopy, sialyl-LewisX-glycosphingolipid-E-Selectin binding, thermodynamic equilibrium calculation
