Document Detail

GPIIIa(90-102) and GPIIIa(631-653) epitopes as markers of conformational changes occurring during the activation of the glycoprotein IIb/IIIa complex.
MedLine Citation:
PMID:  7523118     Owner:  NLM     Status:  MEDLINE    
To evaluate the range of conformational changes in the GPIIIa subunit upon the interaction of GPIIb/IIIa complex with fibrinogen, we employed two polyclonal antipeptide antibodies against synthetic peptides spanning chain segments (90-102) and (631-653) of GPIIIa. The first peptide fragment derives from the region preceding the putative binding site for the RGD sequence, while the second one is located in the vicinity of membrane lipid bilayer. The resting platelets bound about 13,700 and 11,500 molecules of anti-[GPIIIa(90-102)] and anti-[GPIIIa(631-653)] antibodies, respectively. The anti-[GPIIIa(90-102)] antibodies preferentially bound to the active form of GPIIb/IIIa complex. This binding was significantly reduced after dissociation of the complex, indicating that the recognized epitopes became partially hidden in the GPIIIa subunit. In contrast to anti-[GPIIIa(90-102)], the anti-[GPIIIa(631-653)] antibodies reacted optimally with the EDTA-treated GPIIb/IIIa. Upon stimulation of platelets with ADP, the number of binding sites anti-[GPIIIa(631-653)] was reduced 2.8-fold. The binding affinity of anti-[GPIIIa(90-102)] antibodies to the resting and ADP-stimulated platelets differed 4.7-fold, indicating that the stimulation of the platelets with ADP resulted in better exposure of this epitope. This binding was inhibited almost totally by fibrinogen in a dose-dependent fashion. Similarly, fibrinogen inhibited binding of the anti-[GPIIIa(631-653)] antibodies to the platelets. In the reversed system, binding of fibrinogen to platelets was inhibited only to 60% by the anti-[GPIIIa(90-102)] antibodies. Such inhibition of fibrinogen binding was sufficient to block aggregation of ADP-stimulated platelets by the anti-[GPIIIa(90-102)] antibodies in platelet-rich plasma. In contrast, the anti-[GPIIIa(631-653)] potentiated fibrinogen binding by 20%, confirming that there were additional interacting sites for fibrinogen in other regions of the GPIIb/IIIa complex. The presented data indicate that the activation of the fibrinogen receptor is associated with extensive conformational changes in the GPIIIa subunit, detectable by use of antipeptide antibodies recognizing not only the epitopes located next to the putative ligand-binding site but also the epitopes in the vicinity of the platelet membrane lipid bilayer.
J Niewiarowska; C S Cierniewski
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Publication Detail:
Type:  In Vitro; Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  European journal of biochemistry / FEBS     Volume:  224     ISSN:  0014-2956     ISO Abbreviation:  Eur. J. Biochem.     Publication Date:  1994 Sep 
Date Detail:
Created Date:  1994-10-27     Completed Date:  1994-10-27     Revised Date:  2007-07-23    
Medline Journal Info:
Nlm Unique ID:  0107600     Medline TA:  Eur J Biochem     Country:  GERMANY    
Other Details:
Languages:  eng     Pagination:  803-9     Citation Subset:  IM    
Department of Biophysics, Medical University, Lodz, Poland.
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MeSH Terms
Amino Acid Sequence
Blotting, Western
Epitopes / chemistry*
Fibrinogen / metabolism
Molecular Sequence Data
Peptide Fragments / chemistry
Platelet Aggregation
Platelet Membrane Glycoproteins / chemistry*,  metabolism
Protein Conformation
Reg. No./Substance:
0/Epitopes; 0/Peptide Fragments; 0/Platelet Membrane Glycoproteins; 9001-32-5/Fibrinogen

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