Crystal structure of OSCAR D1D2. (A) Crystal structure of free OSCAR D1D2, colored according to secondary structure (β-sheet, magenta; 3₁₀ helix, silver; polyproline-type II helix, cyan). Putative N-glycosylation sites are shown as spheres. Strands are labeled according to standard immunoglobulin-like domain topology. (B) Overlay of D1 of apo-OSCAR (magenta) and THP-bound OSCAR (cyan) to illustrate the shift of the C′ strand in the free receptor (residues 47-55, PLLFRDVSS; shown as sticks) to a D strand in the bound receptor. (C) Overlay of D1 from the collagen-binding LRC receptors OSCAR (magenta), GPVI (blue), and LAIR-1 (green). (D) Overlay of D2 from OSCAR (magenta), GPVI (blue), LILRB4 (orange), and p58-CL42 KIR (brown) to illustrate changes in the AB loop region and the cis vs trans conformation of residue Pro-111 (see supplemental Discussion).