Death and Destruction

teins interfere with apoptosis induced by the action of Fas ligand on immune cells, but no inhibitor of granzyme B activity was previously known. Andrade reported that the rate of binding of 100K to GrB was diffusionlimited, and that the proteins bound with high affinity. But cleavage occurred so slowly that the half-life of the complex averaged 3 hours. If a critical 100K aspartate was mutated, 100K lost its ability to inhibit, and instead was cleaved at an alternative site. As 100K is an important structural protein for the virus, it is present at significant molar excess over GrB. Andrade stated that, in a typical infected cell, this molar excess would ensure an average lag of 141 hours before any GrB activity was free to cleave other substrates. By this time the adenovirus will have replicated and departed from the cell.