VALENCY DEPENDENT PATTERNS OF BINDING OF HUMAN L-SELECTIN TOWARD SIALYL AND SULFATED OLIGOSACCHARIDES OF LE(A) AND LE(X) TYPES - RELEVANCE TO ANTIADHESION THERAPEUTICS

The human L-selectin is known to bind to immobilized 3'-sialyl-Le(x) a nd -Le(a) oligosaccharides both under static and physiological flow co nditions. Here the reactivities toward 3'-sulfated and 3'-sialyl-Le(a) and -Le(x) pentasaccharides are compared by in-vitro binding and inhi bition assays using preparations of human L-selectin-IgG-Fc chimera in which the selectin is predominantly in di- and tetrameric form (pauci valent) or in the form of a complex with anti-IgG (multivalent). Affin ity for the sulfated ligands is marginally greater than for the sialyl ligands, as judged by concentrations required to give 50% inhibition of the multivalent selectin binding to the immobilized sulfated and si alyl ligands. There is a striking difference, however, in the aviditie s of binding of the two L-selectin forms toward the sulfated and sialy l ligands when these are immobilized in the clustered state: the pauci valent selectin gives detectable binding only to the sulfated ligands when these are immobilized as neoglycolipids on plastic microwells (up to 100 pmol immobilized per well) whereas the multivalent L-selectin binds well to both classes of ligand. Moreover, binding of the pauciva lent selectin form is effectively inhibited only by the sulfated ligan d, although binding of the multivalent selectin is inhibitable by both the sulfated and sialyl ligands. Such striking valency-dependent diff erences in ligand binding avidity and inhibitability may be manifest i n vivo with the membrane-bound L-selectin, as marked variations occur in its density of expression on leukocytes. Thus, for the purpose of s electing inhibitors for development of therapeutic anti-inflammatory c ompounds, experimental designs based on the paucivalent L-selectin wou ld more clearly single out compounds with broad spectrum anti-adhesive activities toward the bath the high- and low-avidity interactions of the cell adhesion protein.