Crystallization of Nb2 and GPVI. (A) Structure of Nb2 binding to GPVI. (i) Side view of the GPVI-Nb2 structure. (ii) Top-down view illustrating the domain swap hinge region. A cartoon representation is shown below each figure. Separate GPVI protein subunits are shown in green and cyan, and both Nb2 proteins are shown in yellow and pink. The domain-swapped D2 domains are labeled D2a and D2b for the N- and C-terminal D2 regions, respectively. (B) Comparison of the D2 domains from the non–domain-swapped structure (PDB: 2GI7) (i) and the domain-swapped structure (ii) with major features highlighted. This highlights the differences within the C-C′ hinge region, the C′ β-strand where no electron density was observed for the domain-swapped structure, and the presence of a 3₁₀ helix between βE and F. (C) Enlarged view of the D2 domain-swapped hinge region with the hinge loops colored in green and cyan and the interchain polar contacts, which stabilize this region, shown as red dashes.