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Prepublished online as a Blood First Edition Paper on February 27, 2003; DOI 10.1182/blood-2002-08-2452.
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Blood, 15 June 2003, Vol. 101, No. 12, pp. 4808-4815
HEMOSTASIS, THROMBOSIS, AND VASCULAR BIOLOGY
Major mutations in calf-1 and calf-2 domains of glycoprotein IIb in patients with Glanzmann thrombasthenia enable GPIIb/IIIa complex formation, but impair its transport from the endoplasmic reticulum to the Golgi apparatus
Nurit Rosenberg,
Rivka Yatuv,
Vladimir Sobolev,
Hava Peretz,
Ariella Zivelin, and
Uri Seligsohn
From the Thrombosis and Hemostasis Research Institute, The Chaim Sheba Medical Center, Tel-Hashomer; Sackler Faculty of Medicine, Tel Aviv University; and Department of Plant Sciences, Weizmann Institute of Science, Rehovot, Israel.
The crystal structure of integrin v 3 comprises 3 regions of contact between v and 3. The main contact on v is located in the -propeller while calf-1 and calf-2 domains contribute minor interfaces. Whether or not contacts between calf-1 and calf-2 domains of glycoprotein (GP) IIb ( IIb) and GPIIIa ( 3) play a role in GPIIb/IIIa complex formation has not been established. In this study we analyzed the effects of 2 naturally occurring mutations in calf-1 and calf-2 domains on GPIIb/IIIa complex formation, its processing, and transport to the cell membrane. The mutations investigated were a deletion-insertion in exon 25 located in calf-2 and an in-frame skipping of exon 20 located in calf-1. Mutated GPIIb cDNAs were cotransfected in baby hamster kidney cells with normal GPIIIa ( 3) cDNA. Analysis by flow cytometry failed to demonstrate detectable amounts of GPIIb or GPIIb/IIIa complex on the surface of cells transfected with each mutation, but immunohistochemical staining revealed their intracellular presence. GPIIb was mainly demonstrable as pro-GPIIb by immunoprecipitation of cell lysates expressing each mutation. Differential immunofluorescence staining of GPIIb and cellular organelles suggested that most altered complexes were located in the endoplasmic reticulum. Homology modeling of normal GPIIb based on the v 3 crystal structure revealed similar contacts between v and 3 and between IIb and 3. Introduction of the mutations into the model yielded partial disruption of the normal contacts in the corresponding domains. These data suggest that despite partial disruption of calf-1 or calf-2 domain, GPIIb/IIIa complex is formed but its transport from the endoplasmic reticulum is impaired.

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