Unusual fucoidin-binding properties of chymotrypsinogen and trypsinogen

Previous work (Jones, R. (1987) Cell Biol. Int. Reports 11, 833 and Jones et al. (1988) Development 102, 781-792) has shown that sperm proacrosin (the zymogen form of the acrosomal proteinase acrosin, EC 3.4.21.10) has the capacity to recognize and bind sulphated polysaccharides and that this property is important for the initial stages of fertilization in mammals. To investigate whether this behaviour is specific to proacrosin, a variety of other proteinases (chymotrypsinogen, trypsinogen, thrombin, elastase, plasminogen, pepsin, Streptomyces griseus proteinase and V8 proteinase from Staphylococcus aureus) were immobilized on nitrocellulose and probed with [125I]fucoidin. Only chymotrypsinogen and trypsinogen retained significant amounts of the probe with Kd values of 1.4.10(-6) M and 3.0.10(-5) M, respectively. Proteinase inhibitors were ineffective as blocking agents suggesting that enzymic activity is not involved in recognition. However, the tertiary structure of the proteins is important, since cleavage of intramolecular disulphide bonds with 2-mercaptoethanol reduced binding by 50-60%. Competition experiments with a variety of mono- and polysaccharides suggest that the number and disposition of sulphate groups is critical for interaction with basic residues on the protein. It is concluded that, like proacrosin, chymotrypsinogen and trypsinogen are bifunctional proteins.