title: Proteolytic degradation of the RGD-binding and non-RGD-binding conformers of human platelet integrin glycoprotein IIb/IIIa: clues for identification of regions involved in the receptor's activation.
abstract: The human integrin glycoprotein (GP)IIb/IIIa plays a central role in haemostasis as an inducible receptor for fibrinogen and other RGD-containing adhesive proteins at the platelet plasma membrane. Expression of the fibrinogen receptor on platelet activation involves conformational changes in the quaternary structure of GPIIb/IIIa. Little is known, however, about the nature of this conformational transition. Given that isolated GPIIb/IIIa contains a mixture of RGD-binding and non-RGD-binding heterodimers, we used limited proteolysis as a tool for investigating the structural differences between the two conformers. Comparison of their fragmentation patterns shows that, whereas in the non-RGD-binding form of GPIIb/IIIa the N-terminal half of the heavy chain of GPIIb (GPIIbH) and the central region of GPIIIa are cleaved by endoproteinase Arg-C, these domains associate tightly with one another in the RGD-binding GPIIb/IIIa and are thus protected from proteolysis. In addition, the C-terminal half of GPIIb becomes more susceptible to degradation in the non-RGD-binding GPIIb/IIIa conformer. Our interpretation, in the context of available structural and functional data, is that a major relative reorientation of the GPIIbH and GPIIIa extracellular domains takes place along the subunit interface during the conformational transition of the platelet integrin.
authors.affiliation: Instituto de Química-Física Rocasolano C.S.I.C., Madrid, Spain.
authors.forename: J J
authors.initials: JJ
authors.lastname: Calvete
authors.forename: K
authors.initials: K
authors.lastname: Mann
authors.forename: W
authors.initials: W
authors.lastname: Schäfer
authors.forename: R
authors.initials: R
authors.lastname: Fernandez-Lafuente
authors.forename: J M
authors.initials: JM
authors.lastname: Guisán
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D002846:Chromatography, Affinity; D002850:Chromatography, Gel; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D006868:Hydrolysis; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000378:metabolism*; D010980:Platelet Membrane Glycoproteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D011487:Protein Conformation; D012697:Serine Endopeptidases
chemical_list: D009842:Oligopeptides; D010980:Platelet Membrane Glycoproteins; C047981:arginyl-glycyl-aspartic acid; C044499:submandibular proteinase A; D012697:Serine Endopeptidases