KCS

Caspase-7 serves as one of apoptotic executioners to cleave the majority of cellular substrates in apoptotic cells. The enzyme expressed as a proenzyme is activated by other caspases upon cell death signals. Crystal structures of caspase-7 revealed a large conformational difference of caspase-7 active site before and after activation, meaning that the activation accompanies a large conformational change of loops constituting the active site. In spite of extensive structural and biochemical analyses, however, a detailed molecular mechanism of the caspase activation remains to be solved. Here, we demonstrate that active sites conformation is close correlation between lengths of caspase-7 L2 loops into S2 subsite. We engineered caspase-7 mutagenesis series on L2 loops and crystallized procaspase-7 with its specific inhibitor, Ac-DEVD-CHO. The determined structure showed the first procaspase-7 bound to a specific caspase inhibitor, implying that the engineering itself gave caspase-7 a catalytic activity. Surprisingly, each heterodimeric structure showed different conformations corresponding to the precursor and matured caspase-7. Biochemical analysis with the mutants demonstrated that the length of L2 loop is pivotal for the enzyme activity.