Table 2.
Binding parameters of interactions of soluble receptors with immobilized ligands.
| Ligand | Type I receptor (analyte) | Type II receptor (analyte) | |||||||||||
| ActR-I | ActR-IB | BMPR-IA | BMPR-IB | ActR-II | ActR-IIB | BMPR-II | |||||||
| Mean | SD | Mean | Mean | SD | Mean | SD | Mean | SD | Mean | SD | mean | SD | |
| BMP-2 | |||||||||||||
| kon × 10-4 [M-1s-1] | NB | NB | 3.9 | ± 0.63 | 2.3 | ± 0.56 | NE | NE | NE | ||||
| koff × 103 [s-1] | NB | NB | 1.9 | ± 0.47 | 8.0 | ± 1.38 | > 100 | > 100 | > 100 | ||||
| KD (kin) [nM] | NB | NB | 48 | ± 19.6 | 350 | ± 146 | NE | NE | NE | ||||
| KD (eq) [nM] | NB | NB | NE | NE | 3800 | ± 608 | 3100 | ± 527 | 13000 | ± 2470 | |||
| GDF-5 | |||||||||||||
| kon × 10-4 [M-1s-1] | NB | NB | 0.5 | ± 0.162 | 0.3 | ± 0.09 | NE | NE | NE | ||||
| koff × 103 [s-1] | NB | NB | 17 | ± 1.90 | 1.0 | ± 0.124 | > 100 | > 100 | > 100 | ||||
| KD (kin) [nM] | NB | NB | 3300 | ± 1439 | 300 | ± 123 | NE | NE | NE | ||||
| KD (eq) [nM] | NB | NB | NE | NE | 22000 | ± 2420 | 4700 | ± 658 | 60000 | ± 9600 | |||
| BMP-7 | |||||||||||||
| kon × 10-4 [M-1s-1] | NE | NB | 0.3 | ± 0.05 | 3.1 | ± 0.38 | NE | NE | NE | ||||
| koff × 103 [s-1] | NE | NB | 5.4 | ± 0.70 | 23 | ± 5.84 | > 100 | > 100 | > 100 | ||||
| KD (kin) [nM] | NE | NB | 1900 | ± 589 | 750 | ± 283 | NE | NE | NE | ||||
| KD (eq) [nM] | 58000 | ± 29140 | NB | NE | NE | 880 | ± 61.6 | 2500 | ± 300 | 9100 | ± 1365 | ||
| Activin-A | |||||||||||||
| kon × 10-4 [M-1s-1] | NB | NB | NB | NB | 30 | ± 3.30 | 14 | ± 2.38 | 10 | ± 1.23 | |||
| koff × 103 [s-1] | NB | NB | NB | NB | 44 | ± 10.6 | 9.6 | ± 2.78 | 76 | ± 19.3 | |||
| KD (kin) [nM] | NB | NB | NB | NB | 180 | ± 63.0 | 88 | ± 40.5 | 890 | ± 335 | |||
| KD (eq) [nM] | NB | NB | NB | NB | NE | NE | NE | ||||||
The data obtained from the interaction soluble type I receptor ectodomains (ECDs) with the immobilized ligands were fitted to the 1:1 Langmuir binding model and the KD (kin) (bold) calculated as koff (× 103 s-1)/kon (× 10-4 M-1 s-1). Due to the fast kinetics of the interaction between type II receptors as analyte and the immobilized ligands BMP2, BMP7 and GDF5, the data could only be fitted by equilibrium dose response KD (eq). The dissociation rate constants (koff) of these interactions are >100 (× 103 s-1). All data represent mean values of three repeated measurements using at least six different analyte concentrations.
ActR = activin receptor; BMP(R) = bone morphogenic protein (receptor); GDF = growth and differentiation factor; NB = no binding above background detected; NE = could not be evaluated; SD = standard deviation.