Figure 3.

Disulfide engineering of β-tryptase dimers and tetramers. Tetrameric β-tryptase was engineered such that two of the four protomer interfaces were covalently linked by a disulfide bond. PyMOL was used to measure the distances between the two proposed thiols of Y75C in the small protomer interfaces (A:B and C:D) or I99C in the large protomer interfaces (A:D and B:C). Tetrameric β-tryptase having a mutation at either Y75C or I99C could only dissociate into two distinct disulfide-linked dimers as indicated in the cartoon. The red spheres are the oxygen atoms of Tyr-75. Protomer nomenclature corresponds to that described by Pereira et al. (15).