Fig. 5.

Intersubunit linker cleavage leads to increased exposure of the substrate-binding groove. (A) Comparison of the crystal structures of procaspase-6 zymogen (PDB ID code 3NR2; Left) and mature, unliganded caspase-6 (PDB ID code 2WDP; Right) highlighting the only two tryptophan residues, Trp-57 and Trp-227, as well as the relative location of the intersubunit linker (magenta) and the active site Cys-163. (B) The intrinsic tryptophan fluorescence profiles of caspase-6 mutation variants. Fluorescence emission scans of 305–400 nm were collected after excitation at 295 nm of 3 μM proteins in 10 mM phosphate buffer, pH 7.5, 120 mM NaCl, and 2 mM DTT. The asterisk designates the D to A substitution at the indicated proteolytic cleavage site, rendering that site uncleavable. Data presented here are a representative from three independent experiments.