Allosteric Control of β11-Tryptase by a Redox Active Disulfide Bond

Background: The S1A serine proteases function in many biological processes and contain a conserved disulfide bond near the active site. Results: This disulfide in the S1A mast cell protease, II-tryptase, exists in oxidized and reduced states in the enzyme, which influences the specificity and efficiency of the enzyme. Conclusion: II-Tryptase is regulated by an allosteric disulfide bond. Significance: Other S1A proteases are likely similarly regulated. The S1A serine proteases function in many key biological processes such as development, immunity, and blood coagulation. S1A proteases contain a highly conserved disulfide bond (Cys(191)-Cys(220) in chymotrypsin numbering) that links two -loop structures that define the rim of the active site pocket. Mast cell II-tryptase is a S1A protease that is associated with pathological inflammation. In this study, we have found that the conserved disulfide bond (Cys(220)-Cys(248) in II-tryptase) exists in oxidized and reduced states in the enzyme stored and secreted by mast cells. The disulfide bond has a standard redox potential of -301 mV and is stoichiometrically reduced by the inflammatory mediator, thioredoxin, with a rate constant of 350 m(-1) s(-1). The oxidized and reduced enzymes have different substrate specificity and catalytic efficiency for hydrolysis of both small and macromolecular substrates. These observations indicate that II-tryptase activity is post-translationally regulated by an allosteric disulfide bond. It is likely that other S1A serine proteases are similarly regulated.