Factor XI binding to activated platelets is mediated by residues R(250), K(255), F(260), and Q(263) within the apple 3 domain.
To localize the platelet binding site on factor XI, rationally designed, conformationally constrained synthetic peptides were used to compete with [(125)I]factor XI binding to activated platelets. The major platelet binding energy resided within the sequence of amino acids T(249)-F(260). Homology scanning, using prekallikrein amino acid substitutions within the synthetic peptide T(249)-F(260), identified a major role for R(250) in platelet binding. Inhibition of [(125)I]factor XI binding to activated platelets by the recombinant Apple 3 domain of factor XI and inhibition by unlabeled factor XI were identical, whereas the recombinant Apple 3 domain of prekallikrein had little effect. A "gain-of-function" chimera in which the C-terminal amino acid sequence of the Apple 3 domain of prekallikrein was replaced with that of factor XI was as effective as the recombinant Apple 3 domain of factor XI and unlabeled factor XI in inhibiting [(125)I]factor XI binding to activated platelets. Alanine scanning mutagenic analysis of the recombinant Apple 3 domain of factor XI indicated that amino acids R(250), K(255), F(260), and Q(263) (but not K(252) or K(253)) are important for platelet binding. Thus, the binding energy mediating the interaction of factor XI with platelets is contained within the C-terminal amino acid sequence of the Apple 3 domain (T(249)-V(271)) and is mediated in part by amino acid residues R(250), K(255), F(260), and Q(263).
Ho
D H
DH
Department of Biochemistry, The Sol Sherry Thrombosis Research Center, and Department of Medicine, Temple University School of Medicine, Philadelphia, Pennsylvania 19140, USA.
Baglia
F A
FA
Walsh
P N
PN
D000595:Amino Acid Sequence; D001665:Binding Sites; D001792:Blood Platelets / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D005172:Factor XI / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007457:Iodine Radioisotopes; D008958:Models, Molecular; D008969:Molecular Sequence Data; D015539:Platelet Activation; D016133:Polymerase Chain Reaction; D011288:Prekallikrein / Q000737:chemistry
D007457:Iodine Radioisotopes; D005172:Factor XI; D011288:Prekallikrein