Fig. 3. Structural studies of upstream interactions of TRAFs. (A) The mushroom-shaped trimeric structure of the TRAF domain of human TRAF2 (left: three-fold axis into the page; right: three-fold axis vertical) is shown here in complex with TNFR2. The coiled-coil region (stalk) is shown as yellow helices. The ß-sheet regions of the three TRAF-C domains are shown respectively in blue, green and purple. Bound peptides from TNFR2 are shown as orange arrows, indicating the direction of the peptide chains. The proposed location of the cellular membrane is shown. This figure is modified from (Park et al., 1999). (B) The structural superposition of several TRAF2-interacting receptor peptides is shown using stereo stick models. Nitrogen atoms, blue; oxygen atoms, red; sulfur atoms, green; carbon atoms, yellow (CD40), gray (CD30), green (Ox40), pink (4-1BB), cyan (LMP1) and purple (TNFR2). This figure is adapted from (Ye et al., 1999, Ye et al., 1999). (C) The crystal structure of the trimeric complex between the TRAF domain of TRAF3 and a CD40 peptide bound in a hairpin configuration (Ni et al., 2000). The color-coding of the TRAF domain follows that of (A) and the CD40 peptides are shown as orange arrows. (D) A ribbon diagram of the complex between TRADD and TRAF2 (left, three-fold axis into the page; right, three-fold axis vertical). TRAF2, blue, green and purple; TRADD, magenta, red and yellow. The TRAF2-TRADD interface is more extensive and exhibits higher affinity than TRAF2-receptor-peptide interactions. This figure was adapted from Park et al. (Park et al., 2000).