Table 2 Binding parameters of interactions of soluble receptors with immobilized ligands.

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

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
k _on × 10^-4 [M^-1s^-1]	NB		NB	3.9	± 0.63	2.3	± 0.56	NE		NE		NE
k _off × 10³ [s^-1]	NB		NB	1.9	± 0.47	8.0	± 1.38	> 100		> 100		> 100
K _D (kin) [nM]	NB		NB	48	± 19.6	350	± 146	NE		NE		NE
K _D (eq) [nM]	NB		NB	NE		NE		3800	± 608	3100	± 527	13000	± 2470
GDF-5
k _on × 10^-4 [M^-1s^-1]	NB		NB	0.5	± 0.162	0.3	± 0.09	NE		NE		NE
k _off × 10³ [s^-1]	NB		NB	17	± 1.90	1.0	± 0.124	> 100		> 100		> 100
K _D (kin) [nM]	NB		NB	3300	± 1439	300	± 123	NE		NE		NE
K _D (eq) [nM]	NB		NB	NE		NE		22000	± 2420	4700	± 658	60000	± 9600
BMP-7
k _on × 10^-4 [M^-1s^-1]	NE		NB	0.3	± 0.05	3.1	± 0.38	NE		NE		NE
k _off × 10³ [s^-1]	NE		NB	5.4	± 0.70	23	± 5.84	> 100		> 100		> 100
K _D (kin) [nM]	NE		NB	1900	± 589	750	± 283	NE		NE		NE
K _D (eq) [nM]	58000	± 29140	NB	NE		NE		880	± 61.6	2500	± 300	9100	± 1365
Activin-A
k _on × 10^-4 [M^-1s^-1]	NB		NB	NB		NB		30	± 3.30	14	± 2.38	10	± 1.23
k _off × 10³ [s^-1]	NB		NB	NB		NB		44	± 10.6	9.6	± 2.78	76	± 19.3
K _D (kin) [nM]	NB		NB	NB		NB		*180*	± 63.0	88	± 40.5	*890*	± 335
K _D (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 K _D (kin) (bold) calculated as k _off (× 10³ s^-1)/k _on (× 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 K _D (eq). The dissociation rate constants (k _off) 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.

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ISSN: 1741-7007

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