Three-Dimensional Structure of a Complex between the Death Domains of Pelle and Tube The amino-terminal interaction modules of Pelle and Tube show limited amino acid sequence similarity to death domains, a family of folds identified in proteins

The amino-terminal interaction modules of Pelle and Tube show limited amino acid sequence similarity to death domains, a family of folds identified in proteins Tsan Xiao,* Par Towb,† Steven A. Wasserman,† and Stephen R. Sprang*‡ *The Howard Hughes Medical Institute and Department of Biochemistry that assemble components of apoptotic signaling pathways (Tartaglia et al., 1993; Feinstein et al., 1995). These The University of Texas Southwestern Medical Center Dallas, Texas 75235-9050 include the TNF receptor and Fas, receptor-associated proteins TRADD and FADD, and effector proteases such †Department of Biology University of California at San Diego as Caspase 8 (Baker and Reddy, 1998). Death domains are generally capable of homotypic interactions. StrucLa Jolla, California 92093-0634 tural studies of the death domains of Fas (Huang et al., 1996), P75 neurotrophin receptor (Liepinsh et al., 1997), and FADD (Jeong et al., 1999) reveal a common helical Summary fold that is also characteristic of death effector domains (DED) (Eberstadt et al., 1998) and caspase recruitment The interaction of the serine/threonine kinase Pelle (CARD) domains (Chou et al., 1998; Qin et al., 1999). and adaptor protein Tube through their N-terminal However, death domains display considerable sequence death domains leads to the nuclear translocation of diversity, consistent with the various cellular functions the transcription factor Dorsal and activation of zyin which they participate. The apparent absence of a gotic patterning genes during Drosophila embryogenconserved interaction surface suggests that death doesis. Crystal structure of the Pelle and Tube death mains may associate by a variety of mechanisms. domain heterodimer reveals that the two death doHere, we describe the crystal structure of a death mains adopt a six-helix bundle fold and are arranged domain heterodimer formed by the death domains of in an open-ended linear array with plastic interfaces Pelle and Tube. We have evaluated the functional relemediating their interactions. The Tube death domain vance of the dimer interface by an in vivo assay, using has an insertion between helices 2 and 3, and a site-directed mutants of Pelle and Tube to rescue DroC-terminal tail making significant and indispensable sophila embryos carrying null mutations in pelle or tube contacts in the heterodimer. In vivo assays of Pelle (Letsou et al., 1991; Shelton and Wasserman, 1993). We and Tube mutants confirmed that the integrity of the describe a mode of interaction that may be unique to major heterodimer interface is critical to the activity Tube and Pelle and yet is supported by a scaffold comof these molecules. mon to all death domains.