The fibrinogen RIBS-I epitope (gamma 373-385) appears proximate to the gamma 408-411 adhesive domain but is not involved in interaction between receptor-bound or surface-adsorbed fibrinogen and platelet GPIIbIIIa
Qd. Liu et Mm. Frojmovic, The fibrinogen RIBS-I epitope (gamma 373-385) appears proximate to the gamma 408-411 adhesive domain but is not involved in interaction between receptor-bound or surface-adsorbed fibrinogen and platelet GPIIbIIIa, BBA-PROT ST, 1429(1), 1998, pp. 217-229
Citations number
48
Categorie Soggetti
Biochemistry & Biophysics
Journal title
BIOCHIMICA ET BIOPHYSICA ACTA-PROTEIN STRUCTURE AND MOLECULAR ENZYMOLOGY
The carboxyl terminus of the fibrinogen (Fg) gamma chain (gamma 400-411) is
necessary and sufficient to support platelet aggregation and adhesion. How
ever, a monoclonal antibody (mAb) to the Fg RIBS-I epitope (gamma 373-385),
the anti-Fg-RIBS-I, which binds only to platelet-bound or surface-adsorbed
Fg but not soluble Fg, inhibits platelet aggregation. In this study, we sh
owed that this same antibody also inhibits the adhesion of platelets to Fg-
coated polystyrene beads. We then investigated the mechanisms by which the
anti-Fg-RIBS-I antibody inhibits platelet aggregation and adhesion. The Fg
RIBS-I epitope does not interact with platelet GPIIbIIIa, since recombinant
Fg missing the last four amino acids, the Ala-Gly-Asp-Val, on the carboxyl
terminus of its gamma chains supports neither platelet aggregation nor adh
esion to surfaces, nor GPIIbIIIa binding, while it binds anti-Fg-RIBS-I nor
mally. Purified, soluble GPIIbIIIa (265 kDa) inhibits the binding of both t
he anti-Fg-RIBS-I and 4A5 (a mAb specific to gamma 408-411 of Fg); however,
peptide G13 (1.5 kDa), corresponding to the Fg gamma chain binding domain
on GPIIba (GPIIb300-312), only inhibits the binding of 4A5, and does not af
fect the binding of the anti-Fg-RIBS-I to Fg. The anti-Fg-RIBS-I reduces th
e on-rate of the 4A5 binding to Fg with no measurable changes in the dissoc
iation of the Fg-bound 4A5. These data indicate that the inhibition of plat
elet aggregation and adhesion by the anti-Fg-RIBS-I antibody is due to the
steric hindrance of the Fg gamma 400-411 to platelet GPIIbIIIa. Thus the Fg
RIBS-I epitope (gamma 373-385) does not appear to be involved in direct in
teraction with platelet GPIIbIIIa, leaving the gamma 408-411 of Fg as the s
ole domain mediating platelet aggregation and adhesion. (C) 1998 Elsevier S
cience B.V. All rights reserved.