Fig. 1.
αL I domain structure and detection by flow cytometry. (A) Ribbon diagram of the αL I domain in an open conformation in complex with ICAM-1 domain 1. The β-strands (yellow), α-helices (cyan), and N and C termini are labeled. I-domain MIDAS and ICAM-1 Glu-34 side chains are shown as stick models with oxygen atoms in red. The MIDAS metal ion and the oxygen atoms of two water molecules are shown as gold and red spheres, respectively. All structure diagrams are drawn in pymol (Delano Scientific, San Carlos, CA). (B) Top view of the αL I domain. The Cα traces, key side chains as sticks, and MIDAS metal ions as large spheres are in magenta (closed) and yellow (open); oxygens are in red. Primary coordinations are shown as dashed lines. (C) The Cα trace and ratchet side chains (Leu-289, Phe-292, Leu-295 shown in stick models) for the closed (magenta), intermediate (green), and open (yellow) conformations of the α7-helix are depicted. The structure of the α7-helix of the closed αL I domain was modeled based on the crystal structure of Protein Data Bank ID codes 1LFA and 1ZON; the structure of the α7-helix of the open αL I domain (Protein Data Bank ID code 1MQ9) was modeled as described (7). (D) Detection by immunofluorescence before (thin lines) and after (thick lines) induction of anti-c-myc antibody 9E10, I domain-specific antibody MEM83, I domain activation-dependent antibody AL-57, and ICAM-1-Fcγ. The percentages of the cells within the gated regions are shown.