Characterization of a human coagulation factor Xa-binding site on Viperidae snake venom phospholipases A2 by affinity binding studies and molecular bioinformatics

Table 1 FXa binding kinetic parameters and effect on prothrombinase activity of Viperidae SVPLA₂

PLA₂	<k_on>(M^-1s^-1)	<k_off> (s^-1)	<K_d^app>[nM]	IC₅₀[nM]	pI*
CBc	(3.2 ± 0.2) × 10⁵	(1.6 ± 0.4) × 10^-4	0.6 ± 0.3	0.7 ± 0.3	8.74
MtxII	(10.4 ± 0.3) × 10⁶	(1.78 ± 0.4) × 10^-2	1.8 ± 0.9	3 ± 1	9.10
CbII	(4.2 ± 2.5) × 10⁵	(8.5 ± 2) × 10^-3	20 ± 3	20 ± 4	8.96
AtxA	(2.2 ± 0.3) × 10⁵	(7 ± 1) × 10^-3	30 ± 2	25 ± 5	8.35
CBa ₂	(2.9 ± 0.4) × 10⁵	(1.5 ± 0.2) × 10^-2	52 ± 4	41 ± 5	8.74
VRV-PLVIII	(4.5 ± 0.4) × 10⁴	(2.6 ± 0.4) × 10^-2	578 ± 15	130 ± 20	8.35
b *Ahp*	(4 ± 1.5) × 10⁴	(1.6 ± 0.3) × 10^-2	400 ± 20	90 ± 10	8.71
*Vbb*	(3 ± 0.5) × 10⁴	(2.5 ± 0.4) × 10^-2	830 ± 15	90 ± 30	8.64
AGTX	NB	NB	NB	>10 000	5.43
CA	NB	NB	NB	>10 000	-
*Catx*	NB	NB	NB	>10 000	4.64
CbI	NB	NB	NB	>10 000	4.86
Reduced and carboxymethylated CBc	NB	NB	NB	nd	nd
hsPLA ₂	(2.0 ± 0.8) × 10⁶	(2.9 ± 1) × 10^-2	14 ± 2	9 ± 2	9.38

*: estimated
NB: non-binding
Nd: not determined
<K_d^app> = <koff>/<kon>
The IC₅₀ value corresponds to 50% inhibition of thrombin generation in the absence of PL for the different SVPLA₂.