Abstract
The platelet membrane glycoprotein IIb X IIIa heterodimer complex (GPIIb X IIIa) is the platelet receptor for adhesive proteins, containing binding sites for fibrinogen, von Willebrand factor, and fibronectin on activated platelets. GPIIb X IIIa also appears to be a member of a family of membrane adhesive protein receptors that plays a major role in cell-cell and cell-matrix interactions. GPIb is the larger component of this platelet receptor and is composed of two disulfide-linked subunits. In this report we describe the analysis of cDNA clones for human GPIIb that were isolated from a lambda gt11 expression library prepared using RNA from HEL cells. A total of 3.3 kilobases of cDNA was sequence, revealing a continuous open reading frame encoding both GPIIb subunits. The cDNA encodes 1039 amino acids: 137 constituting the smaller subunit, 871 constituting the larger subunit, and 30 constituting an NH2-terminal signal peptide. No homology was found between the larger and smaller subunits. The smaller subunit contains a 26-residue hydrophobic sequence near its COOH terminus that represents a potential transmembrane domain. Four stretches of 12 amino acids present in the larger subunit are homologous to the calcium binding sites of calmodulin and troponin C. Northern blot analysis using HEL cell RNA indicated that the mature mRNA coding for GPIIb is 4.1 kilobases in size. A comparison of the GPIIb coding region with available cDNA sequences of the alpha-chains of the vitronectin and fibronectin receptors revealed 41% DNA homology and 74% and 63% amino acid homology, respectively. Our data establish the amino acid sequence for the human platelet glycoprotein IIb and provide additional evidence for the existence of a family of cellular adhesion protein receptors.
Highlights
From the #Divisionof Hematology, The Children’s Hospital of Philadelphia, thellHematology-OncologySection, The Hospital of the University of Pennsylvania, and the Departments of Pediatrics, Human Genetics, and Medicine, The Universityof Pennsylvania School of Medicine, Philndelphia, Pennsylvania 19104
We have isolated and determined the DNA sequence for dimer complex requires the presence of submicromolar conhuman platelet GPIIb using cDNA obtained from an HEL centrations of ionic calcium
Confirmation that these clones repre- 1985). The basis for this requirement is not clear, sent platelet GPIIb cDNA isbased on two lines of evidence
Summary
GPIIb is the larger component of approximately 136,000 on SDS-polyacrylamide gels and conthis platelet receptor anids composed of two disulfide- tains two disulfide-linked components, a larger subunit of M , linked subunits.In this report dweescribe the analysis of cDNA clones for human GPIIb that were isolated from a Xgt 11expression library prepared usingRNA from HEL cells. The abbreviations used are: GPIIb, glycoprotein IIb; GPIIIa, glycoprotein IIIa; SDS, sodium dodecyl sulfate; FN, fibronectin; VN, vitronectin; IPTG, isopropyl-1-thio-P-D-galactopyranosidkeb;, kilobase; bp, base pair Briefly,lystates from IPTG-stimulated or unstimulated bacteria and suspensionofs washed human platelets plateletfactor 4 from a cDNA library constructed i n the were dissolved in 1% sodium dodecyl sulfate (SDS) and electrophoexpressionvector Xgtll using HEL cell mRNA.
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