Cell adhesion mechanisms: modeling using derivatized beads and sea urchin cell systems

Agarose beads derivatized with amino acids, peptides, carbohydrates and lectins were used to systematically determine what types of molecules, isolated from all others, can make adhesive bonds strong enough to hold cell-like beads together. The results indicated that strong adhesion occurred when at least one of the two members of certain bead pairs was derivatized with molecules that were dimers or trimers but not monomers. Also, beads derivatized with phosphorylated amino acids, but not their non-phosphorylated counterparts, adhered to beads derivatized with positively charged peptides. Adhesion was sensitive to ionic strength and pH of the medium. It was proposed that adhesion occurred between the phosphate groups of the phosphoamino acids and amino and guanidinium groups of the peptides. Cooperative bonding can explain the stability of the adhesion observed in this system. Information gained from the bead modeling work was used to design experiments to examine the role of phosphorylated molecules in modulating adhesion in sea urchin systems. Phosphoamino acids inhibited sperm-egg interaction, but not reaggregation of blastula cells. Inhibitors of alkaline phosphatase, however, did inhibit reaggregation. The results suggest that cell surface phosphorylated molecules may modulate cellular adhesiveness, in some systems promoting, while in others inhibiting adhesion.