The Drosophila inhibitor of apoptosis protein DIAP1 exists in an auto-inhibited conformation, unable to suppress the effector caspase drICE. Auto-inhibition is disabled by caspase-mediated cleavage of DIAP1 after Asp20. The cleaved DIAP1 binds to mature drICE, inhibits its protease activity, and, presumably, also targets drICE for ubiquitylation. DIAP1-mediated suppression of drICE is effectively antagonized by the pro-apoptotic proteins Reaper, Hid, and Grim (RHG). Despite rigorous effort, the molecular mechanisms behind these observations are enigmatic. Here we report a 2.4 Å crystal structure of uncleaved DIAP1-BIR1, which reveals how the amino-terminal sequences recognize a conserved surface groove in BIR1 to achieve auto-inhibition, and a 3.5 Å crystal structure of active drICE bound to cleaved DIAP1-BIR1, which provides a structural explanation to DIAP1-mediated inhibition of drICE. These structures and associated biochemical analyses, together with published reports, define the molecular determinants that govern the interplay among DIAP1, drICE and the RHG proteins.
ASJC Scopus subject areas
- Biochemistry, Genetics and Molecular Biology(all)
- Physics and Astronomy(all)