title: Role of the alpha-subunit 326GRV sequence in the surface expression of fibrinogen and vitronectin receptors.
abstract: The platelet GPIIb-GPIIIa heterodimer (integrin alphaIIbbeta3) binds fibrinogen with high affinity in response to activation by agonists, leading to platelet aggregation and formation of a hemostatic plug. The 326GRV motif in GPIIb is highly conserved in the alpha-subunit of other integrins, suggesting that it might play an important functional role. Moreover, Arg327-->His substitution in GPIIb has been associated with defective platelet surface expression of GPIIb-IIIa and thrombasthenic phenotype. This work aimed at elucidating whether the absence of Arg327 or its substitution by His was responsible for the impaired surface expression of GPIIb-IIIa complexes. Transfection of cDNA encoding [Ala327]GPIIb, [Gln327]GPIIb, or [Phe327]GPIIb into Chinese hamster ovary cells inherently expressing GPIIIa permitted surface exposure of GPIIb-IIIa complexes, whereas [Glu327]GPIIb did not. These observations indicate that it is not the loss of [Arg327]GPIIb but the presence of His327 or a negatively charged residue like Glu at position 327 of GPIIb that prevents the surface exposure of GPIIb-IIIa heterodimers. In contrast, changing Gln344, the homologue to Arg327 in the alpha-subunit of the vitronectin receptor, to His did not prevent the surface expression of alphav-GPIIIa complexes. Thus the conformational constraint imposed by His327 seems to be rather specific for the heterodimerization and/or processing of GPIIb-IIIa complexes.
authors.affiliation: Department of Pathophysiology and Human Molecular Genetics, Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas, Velázquez 144, 28006-Madrid, Spain.
authors.forename: M
authors.initials: M
authors.lastname: Ferrer
authors.forename: M S
authors.initials: MS
authors.lastname: Ayuso
authors.forename: N
authors.initials: N
authors.lastname: Butta
authors.forename: R
authors.initials: R
authors.lastname: Parrilla
authors.forename: C
authors.initials: C
authors.lastname: González-Manchón
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D001120:Arginine; D001483:Base Sequence; D016466:CHO Cells; D002462:Cell Membrane / Q000502:physiology; D006224:Cricetinae; D017931:DNA Primers; D005786:Gene Expression Regulation; D006639:Histidine; D006801:Humans; D046911:Macromolecular Substances; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics*; D017354:Point Mutation; D016133:Polymerase Chain Reaction; D019030:Receptors, Vitronectin / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics*; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014162:Transfection
chemical_list: D017931:DNA Primers; D046911:Macromolecular Substances; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D019030:Receptors, Vitronectin; D011994:Recombinant Proteins; D006639:Histidine; D001120:Arginine