Abstract
We have investigated the structural features of sulfated fucose-containing polysaccharides which are responsible for their selective binding to Strongylocentrotus purpuratus bindin. The data presented demonstrate that the sulfate esters and a molecular weight in excess of approximately 15,000 are required for high affinity binding of the fucans to bindin. Desulfation destroys the binding activity of the fucans, which can be fully restored by chemical resulfation. Fucan fragments of an average molecular weight of 15,000 were nearly as active as the starting material (Mr 10(6)). The observed IC50 value for fragments of Mr congruent to 10,000 and Mr congruent to 5,000 were 1 and 2 orders of magnitude higher, respectively. The binding of fucoidan to bindin is stable in high salt (50% at 1.2 M NaCl) whereas the binding of fucoidan to DEAE-cellulose or polylysine is inhibited by the concentrations of salt normally found in sea water (50% at 0.2 and 0.5 M NaCl, respectively). This result suggests that the binding mechanism is not a simple ionic interaction and that hydrogen bonding and cooperativity may also be important determinants of the binding mechanism. We also found that polyvinyl sulfate binds to bindin with high affinity and inhibits the bindin-mediated agglutination of sea urchin eggs. The results of these investigations suggest that the spatial orientation of the sulfate esters plays a critical role in determining the selectivity of sulfated polysaccharide binding and that the polysaccharide backbone does not play a direct role in the binding mechanism.
Highlights
We have investigated the structural features of sulfated fucose-containing polysaccharides which are responsible for their selective binding to Strongylocentrotus purpuratusbindin
Other sulfated fucose-containing polysaccharides such as fucoidan and theegg jelly fucan bind to bindin with high affinity (14).Fucoidan has acomposition similar to thefucan purified from the egg surface by affinity chromatography on bindin
Sulfate esters appear to be important for the interaction of bindin and fucoidan, since solvolytic desulfation results in the inactivation of fucoidan (14).This interpretation, is complicated by the fact that the desulfation procedure results in some degree of depolymerization of the polysaccharide
Summary
Resulfated fucan and the startingmaterial are very similar, it Effect of Desulfation and Chemical Resulfation on Fucan Binding-Previous studies have indicated that aftersolvolysis desulfated fucoidan is a very poor inhibitor of ''51-fucoidan binding to bindin particles(14). The apparent surface charge of desulfated fucoidan and egg jelly fucan are greatly reduced, as measured by the toluidine blue metachromatic shift titration point. This result is consistent withthe decrease in sulfateester contentmeasured for fucoidan and egg jelly fucan (Table I). Incubation of desulfated fucoidan with lower concentrations of chlorosulfonic acid and at lower temperature (C1S04:fucose(2.5:1), 0 "C) results in an intermediate degree of resulfation (Table I).The chemical sulfation reaction does not detectably change the gel filtration profile of the fucan preparations: fucoidan still runs in the Vowith no release of smaller molecular weight sugars, and desulfated fucoidan's 2 peaks elute at the same positions: slightly after the Vo and immediately before the V i (data not shown). The relative affinity of the fragmentsforbindin was determined by measuring their ability to compete for the binding of '251-fucoidanto
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