The tetramer structure of GPIbβ_Eabc shows a binding interface between GPIbβ_E-derived C-terminal cap region and GPIX_E-derived convex loops. (A) Cartoon diagram showing 2 views of the GPIbβ_Eabc tetramer structure related by a 90-degree rotation. The N-termini (N) of the molecules are at the peripheral of the tetramer, and the C-termini (C) are all located in proximity at the bottom of the lower panel. Sequences derived from GPIbβ_E are colored in blue and those derived from GPIX_E in magenta. The side chain of GPIbβ-Tyr106 at each interface is shown in green as stick. (B) A close-up view of the interface between 2 GPIbβ_Eabc molecules (GPIbβ_E-derived residues in blue and GPIX_E-derived residues in magenta). Interacting side chains are labeled and colored accordingly, and underlined residues were subject to mutagenesis.