title: Structural mechanisms of DIAP1 auto-inhibition and DIAP1-mediated inhibition of drICE.
abstract: 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.
authors.affiliation: Ministry of Education Protein Science Laboratory, Center for Structural Biology, School of Life Sciences and School of Medicine, Tsinghua University, Beijing, China.
authors.forename: Xiaochun
authors.initials: X
authors.lastname: Li
authors.forename: Jiawei
authors.initials: J
authors.lastname: Wang
authors.forename: Yigong
authors.initials: Y
authors.lastname: Shi
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D020169:Caspases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D003460:Crystallization; D015536:Down-Regulation; D029721:Drosophila Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics; D015971:Gene Expression Regulation, Enzymologic; D051034:Inhibitor of Apoptosis Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D011485:Protein Binding; D017434:Protein Structure, Tertiary
chemical_list: C111891:DIAP1 protein, Drosophila; D029721:Drosophila Proteins; D051034:Inhibitor of Apoptosis Proteins; D020169:Caspases; C109171:drICE protein, Drosophila