title: Modeling and functional analysis of the interaction between von Willebrand factor A1 domain and glycoprotein Ibalpha.
abstract: Binding of the von Willebrand factor (vWF) A1 domain to the glycoprotein (GP) Ib-IX-V complex mediates platelet adhesion to reactive substrates under high shear stress conditions, a key event in hemostasis and thrombosis. We have now used the known three-dimensional structure of the A1 domain to model the interaction with the GP Ibalpha sequence 271-279, which has previously been implicated in ligand binding. Docking procedures suggested that A1 domain residues in strand beta3 and preceding loop (residues 559-566) as well as in helix alpha3 (residues 594-603) interact with Asp residues 272, 274, 277 and sulfated Tyr residues 278 and 279 in GP Ibalpha. To verify this model, 14 mutant A1 domain fragments containing single or multiple side chain substitutions were tested for their ability to mediate platelet adhesion under flow. Each of the vWF residues Tyr(565), Glu(596), and Lys(599) proved to be strictly required for A1 domain function, which, in agreement with previous findings, was also dependent on Gly(561). Moreover, an accessory functional role was apparent for a group of positively charged residues, including Arg at positions 629, 632, 636 and Lys at positions 643 and 645, possibly acting in concert. There was, however, no evidence from the model that these residues directly participate in forming the complex with GP Ibalpha. These results provide a partial model of the vWF-GP Ibalpha interaction linked to the manifestation of functional activity in platelet adhesion.
authors.affiliation: Roon Research Center for Arteriosclerosis and Thrombosis, Division of Experimental Hemostasis and Thrombosis, Department of Molecular and Experimental Medicine, The Scripps Research Institute, La Jolla, California 92037, USA.
authors.forename: S
authors.initials: S
authors.lastname: Vasudevan
authors.forename: J R
authors.initials: JR
authors.lastname: Roberts
authors.forename: R A
authors.initials: RA
authors.lastname: McClintock
authors.forename: J A
authors.initials: JA
authors.lastname: Dent
authors.forename: R
authors.initials: R
authors.lastname: Celikel
authors.forename: J
authors.initials: J
authors.lastname: Ware
authors.forename: K I
authors.initials: KI
authors.lastname: Varughese
authors.forename: Z M
authors.initials: ZM
authors.lastname: Ruggeri
mesh_terms: D000596:Amino Acids / Q000737:chemistry; D001792:Blood Platelets / Q000737:chemistry / Q000378:metabolism; D002448:Cell Adhesion; D003198:Computer Simulation; D004305:Dose-Response Relationship, Drug; D006801:Humans; D008958:Models, Molecular; D016296:Mutagenesis; D019038:Platelet Glycoprotein GPIb-IX Complex / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000378:metabolism; D014841:von Willebrand Factor / Q000737:chemistry* / Q000378:metabolism
chemical_list: D000596:Amino Acids; D019038:Platelet Glycoprotein GPIb-IX Complex; D011994:Recombinant Proteins; D014841:von Willebrand Factor