Biomedical Engineering Reference
In-Depth Information
Table 6.2
Selected monoclonal antibodies for the detection of RIBS of fi brinogen
Name
Epitope
Surface
Reference
I. N-terminal regions
9F9
γ
112-119
Polystyrene
78
18C6
β
1-42
PMMA/PBMA
79
155B6
α
95-98
Polystyrene
78
II. C-terminal regions
2G5
γ
373-385
Polystyrene
77,78
4-2
γ
392-406
PMMA/PBMA
79
4A5
γ
402-411
PMMA/PBMA
79
Note
: PMMA: polymethylmethacrylate; PBMA: polybutylmethacrylate.
non-activated state.
62
One of the platelet recognition sites of fi brinogen, like
the crosslinking ones, is located in γ chains, whereas the others are in Aα
chains. The dodecapeptide at residue 400-411 of the γC region constitutes a
binding domain for GPIIb-IIIa.
4,65-69
A common Arg-Gly-Asp-X (RGDX)
sequence has been identifi ed in two different receptor-recognition regions
of the Aα chain, one near the C-terminal and the other near the central E
domain.
4,65-68,70
The binding strength of fi brinogen to GPIIb-IIIa, characterized by equi-
librium dissociation constant K
d
, is generally on the order of sub-µM.
71,72
As
a comparison, K
d
between RGD containing peptides and the GPIIb-IIIa
receptor can be regarded as medium strength, in the range of mM to µM.
73
The force for a single pair of ligand-receptor interactions falls into three
sets ranging from 70 to 310 pN.
74
Experimental measurements reveal that
the binding of fi brinogen to GPIIb-IIIa is at least biphasic.
71,72,75
The dimeric
nature of fi brinogen renders it a 'molecular bridge' promoting platelet
aggregation, as platelets can bind to each outer end of fi brinogen. In this
way, hemostasis is restored as an effective seal is rapidly formed at vascular
injury sites.
4,76
The bound fi brinogen experiences receptor-induced conformational
changes and exposes neo-epitopes. These so-called receptor-induced bind-
ing sites (RIBSs) include Arg
95
-Phe
98
of the Aα chain, and Glu
112
-Gln
119
and Arg
375
-Lys
385
of the γ chain when fi brinogen is adsorbed on hydropho-
bic polystyrene surface.
77,78
Monoclonal antibodies (mAb) are developed
and commonly used to recognize these RIBSs. Subsequent studies reveal
that exposed epitopes of adsorbed fi brinogen depend on the physiochemi-
cal properties of the surfaces, the packing density and hence the confor-
mational states of surface-bound fi brinogen.
79,80
The locations of selected
known epitopes recognized by mAbs are summarized in Table 6.2. This
information can be used to examine the extent to which platelet adhesion,
