Deciphering structural and functional roles of disulfide bonds in decorsin

Decorsin, an antagonist of integrin glycoprotein IIb/IIIa, contains Arg-Gly-Asp (RGD) sequence and three disulfide bridges. The function of RGD sequence has already been well defined, but the roles of conserved disulfide bonds in antihemostatic proteins still remain unclear. Herein we use the fusion expression and characterization of mutant decorsin to study the functions of disulfide bonds in protein structure, stability and biological activity. The purified protein shows an apparent inhibition of activity to platelet aggregation induced by ADP with IC50 of 500 nM. The removal of cys7-cys15 (from cysteine to serine) at the N-terminal causes a thirty-fold decrease of the inhibition activity with IC50 of 15 μM, whereas the mutation of cys22-cys38 at the C-terminal completely impairs the biological activity of decorsin. The overall secondary and tertiary structures of decorsin are disrupted inevitably without disulfide bonds. Using a domain insertion mutation, the retaining of RGD loop and the adjacent disulfide bond produces a week antihemostatic activity of decorsin. This reveals that the overall structure of decorsin stabilized by the three conserved disulfide bridges is cooperative for antihemostatic function. Our study on the effect of disulfide bonds together with RGD-sequence on the protein function is helpful for structure-based drug design of antithrombotic research.