KINETICS AND LOCUS OF FAILURE OF RECEPTOR-LIGAND-MEDIATED ADHESION BETWEEN LATEX SPHERES .2. PROTEIN-PROTEIN BOND

In an extension of the previous paper, we describe the force dependenc e of break-up of doublets of latex spheres cross-linked by protein G-l gG bonds via the Fc region of the antibody, The receptor, the monoclon al Bear-1 antibody, was either covalently linked to 4.75-mu m aldehyde /sulfate (A/S) latex spheres in a one-step reaction, or physically ads orbed to the 4.63-mu m carboxyl-modified latex spheres used in Part I of this paper, The spheres were suspended in 19% buffered Dextran 40 c ontaining the ligand, the bivalent recombinant protein G (Gamma-Bind G ), and observed in the counter-rotating cone and plate Rheoscope. Brea k-up of doublets, tracked individually under the microscope, as well a s in populations of 50-150 particles, was studied over a range of norm al force from 20 to 260 pN, In individual particle studies, the fracti on of doublets of spheres with covalently linked IgG breaking up in th e first 10 rotations, increased from 16% in the low-force to 63% in th e high-force range, In population studies, the fraction broken up incr eased with duration and magnitude of the applied force, and decreased with increasing ligand concentration, Moreover, doublets of physically adsorbed IgG spheres required significantly lower force than doublets of covalently linked IgG spheres for the same degree of break-up, pos sibly because of surface detachment of IgG molecules rather than ruptu re of receptor-ligand bonds, Computer simulation, using the Bell stoch astic model of break-up and a Poisson distribution for the number of b onds, described in Part I, showed that the parameters of the protein-p rotein bond differed significantly from those of the carbohydrate-prot ein bond studied in Part I of this paper, the former being much more r esponsive to force than the latter.