Homology model of GPVI. In the main portion of the figure, an α carbon (C^α) trace of the Lir-1 molecule, a member of the Ig gene superfamily and a close homolog of GPVI, is depicted as a tubular representation. This representation is derived from the crystal structure of Lir-1 (PDB 1G0X) and is rendered using the program Cn3D (version 4.1) produced by the National Center for Biotechnology Information (Bethesda, MD) and distributed freely to the public. In the main figure, the extracellular domains D1 and D2 are labeled. In the enlargement in the bottom right corner (inset), selected amino residues of GPVI that are positional homologs to those in Lir-1 are labeled. These residues are all situated in 2 adjacent hydrophilic loops in the ligand binding region of D1. The first hydrophilic loop contains residues thought to participate in ligand binding: V54, D55, L56, R58, E60, and K61. An adjacent hydrophilic loop contains, at its apex, the consensus N-linked glycosylation site represented by residues N92 and S94.