title: Physical proximity and functional association of glycoprotein 1balpha and protein-disulfide isomerase on the platelet plasma membrane.
abstract: Platelet function is influenced by the platelet thiol-disulfide balance. Platelet activation resulted in 440% increase in surface protein thiol groups. Two proteins that presented free thiol(s) on the activated platelet surface were protein-disulfide isomerase (PDI) and glycoprotein 1balpha (GP1balpha). PDI contains two active site dithiols/disulfides. The active sites of 26% of the PDI on resting platelets was in the dithiol form, compared with 81% in the dithiol form on activated platelets. Similarly, GP1balpha presented one or more free thiols on the activated platelet surface but not on resting platelets. Anti-PDI antibodies increased the dissociation constant for binding of vWF to platelets by approximately 50% and PDI and GP1balpha were sufficiently close on the platelet surface to allow fluorescence resonance energy transfer between chromophores attached to PDI and GP1balpha. Incubation of resting platelets with anti-PDI antibodies followed by activation with thrombin enhanced labeling and binding of monoclonal antibodies to the N-terminal region of GP1balpha on the activated platelet surface. These observations indicated that platelet activation triggered reduction of the active site disulfides of PDI and a conformational change in GP1balpha that resulted in exposure of a free thiol(s).
authors.affiliation: Centre for Thrombosis and Vascular Research, School of Pathology, University of New South Wales and the Department of Haematology, Prince of Wales Hospital, Sydney NSW 2052, Australia.
authors.forename: J K
authors.initials: JK
authors.lastname: Burgess
authors.forename: K A
authors.initials: KA
authors.lastname: Hotchkiss
authors.forename: C
authors.initials: C
authors.lastname: Suter
authors.forename: N P
authors.initials: NP
authors.lastname: Dudman
authors.forename: J
authors.initials: J
authors.lastname: Szöllösi
authors.forename: C N
authors.initials: CN
authors.lastname: Chesterman
authors.forename: B H
authors.initials: BH
authors.lastname: Chong
authors.forename: P J
authors.initials: PJ
authors.lastname: Hogg
mesh_terms: D000906:Antibodies / Q000276:immunology; D001792:Blood Platelets / Q000201:enzymology / Q000378:metabolism*; D002462:Cell Membrane / Q000201:enzymology / Q000378:metabolism; D006801:Humans; D008970:Molecular Weight; D015539:Platelet Activation; D010974:Platelet Aggregation; D010980:Platelet Membrane Glycoproteins / Q000378:metabolism*; D019704:Protein Disulfide-Isomerases / Q000097:blood* / Q000276:immunology; D013438:Sulfhydryl Compounds / Q000097:blood / Q000737:chemistry; D014841:von Willebrand Factor / Q000378:metabolism
chemical_list: D000906:Antibodies; D010980:Platelet Membrane Glycoproteins; D013438:Sulfhydryl Compounds; D014841:von Willebrand Factor; D019704:Protein Disulfide-Isomerases