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Table 1 Binding parameters of interactions of soluble ligands with immobilized receptor ectodomains (ECDs)

From: Receptor oligomerization and beyond: a case study in bone morphogenetic proteins

Ligand (analyte) Type I receptor (immobilized) Type II receptor (immobilized)
  ActR-I ActR-IB BMPR-IA BMPR-IB ActR-II ActR-IIB BMPR-II
  Mean Mean Mean SD Mean SD Mean SD Mean SD Mean SD
BMP-2             
k on × 10-4 [M-1s-1] NB NB 50 ± 12.1 25 ± 4.37 370 ± 66.6 280 ± 33.6 150 ± 25.5
k off × 103 [s-1] NB NB 0.4 ± 0.09 0.7 ± 0.09 88 ± 23.8 18 ± 4.68 70 ± 19.6
K D (kin) [nM] NB NB 0.8 ± 0.37 2.7 ± 0.82 14 ± 6.31 6.3 ± 2.39 45 ± 20.3
K D (eq) [nM] NB NB NE   NE   24 ± 1.92 9.0 ± 1.17 59 ± 10.0
GDF-5             
k on × 10-4 [M-1s-1] NB NB 23 ± 5.98 39 ± 4.68 140 ± 15.4 110 ± 19.8 110 ± 20.9
k off × 103 [s-1] NB NB 4.3 ± 0.77 0.5 ± 0.16 28 ± 4.48 4.5 ± 0.59 38 ± 8.74
K D (kin) [nM] NB NB 19 ± 8.36 1.3 ± 0.56 20 ± 5.40 4.0 ± 1.24 36 ± 15.1
K D (eq) [nM] NB NB NE   NE   32 ± 3.84 5.6 ± 0.90 46 ± 8.28
BMP-7             
k on × 10-4 [M-1s-1] NE NB 14 ± 2.24 11 ± 2.42 120 ± 20.4 140 ± 30.8 96 ± 14.4
k off × 103 [s-1] NE NB 7.9 ± 1.19 1.0 ± 0.18 6.2 ± 0.69 9.0 ± 1.26 24 ± 6.24
K D (kin) [nM] > 500* NB 58 ± 18.0 9.0 ± 3.87 5.1 ± 1.43 6.5 ± 2.34 25 ± 10.3
K D (eq) [nM] > 500* NB NE   NE   8.0 ± 0.48 9.2 ± 1.28 40 ± 5.20
Activin-A             
k on × 10-4 [M-1s-1] NB NB NB   NB   130 ± 23.4 160 ± 22.4 53 ± 7.95
k off × 103 [s-1] NB NB NB   NB   7.5 ± 1.65 1.7 ± 0.14 29 ± 6.96
K D (kin) [nM] NB NB NB   NB   5.7 ± 2.28 1.1 ± 0.24 59 ± 24.2
K D (eq) [nM] NB NB NB   NB   6.0 ± 0.54 2.1 ± 0.15 24 ± 4.08
  1. The data obtained from measurements with immobilized type I receptor ECDs were fitted to a kinetic model (1:1 Langmuir binding) from which K D (kin) (bold) is calculated as k off (× 103 s-1)/k on (× 10-4 M-1 s-1). Due to low but significant binding of BMP7 to AR-I, affinities could not be evaluated exactly but are estimated to be higher than 500 nM (bold, asterisks). The data obtained from ligand binding to immobilized type II receptors were best fitted by equilibrium dose response K D (eq) (bold). For this interaction the calculation of K D (kin) (bold, italic) revealed minor differences (<twofold). All data represent mean values of at least three repeated measurements using six different ligand concentrations.
  2. 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.