Structure and alignment of the β-propeller domain of αIIb. (A) Human and mouse sequence alignment of the β-propeller domain. The boxes indicate the small loop structures of each β-sheet domain, and the asterisks indicate amino acid difference between human and mouse sequences. (B) Abbreviation of each human-mouse chimeric αIIb/human β3. m(X)H; human αIIb (black) carrying mouse sequences (white) from the N-terminus to the X region. Hm(X)H; human αIIb was exchanged with the only X region for the corresponding sequence of mouse αIIb. H(X)m; mouse αIIb carrying human sequences from the N-terminus to the X region. mH(X-Y)m; mouse αIIb was exchanged with the region of X to Y for the corresponding human αIIb. m(β-propeller)H; human αIIb was exchanged with the entire β-propeller domain of αIIb for the corresponding mouse αIIb. (C) Assessment of PA Abs binding to mutated αIIbβ3-expressing cells. Binding of PA Abs (horizontal) was analyzed in a subset of CD61 highly positive cells denoted by the rectangle (R7) in the dot blots.