Table 2.

Summary of kinetic and thermodynamic binding measurements for IL-13 mutants binding to IL-13Rα1 and IL-13Rα2.

SPR Kinetics/Equilibrium Affinity
IL-13 Mutant	IL-13Rα1 immobilized			IL-13Rα2 immobilized
	kon(M−1s−1)	koff (s−1)	KD (M−1)	kon(M−1s−1)	koff (s−1)	KD (M−1)
IL-13WT	2.35×106	3.97×10−3	1.69×10−9	1.22×108	1.93×10−6	1.58×10−14
IL-13 R11A	1.87×106	4.87×10−3	2.60×10−9
IL-13 I14A			3.17×10−7	1.79×107	1.52×10−4	8.47×10−12
IL-13 E15A	2.82×106	4.45×10−3	1.58×10−9
IL-13 V18A	3.26×106	4.43×10−3	1.36×10−9
IL-13 M33A			8.65×10−8
IL-13 D87A	2.74×106	7.51×10−3	2.74×10−9
IL-13 T88A	2.80×106	4.88×10−3	1.75×10−9
IL-13 K89A			1.28×10−8
IL-13 I90A			1.70×10−8
IL-13 E91A			1.35×10−8
IL-13 L101A	3.53×106	4.63×10−3	1.31×10−9
IL-13 K104A			3.93×10−7	9.64×106	2.71×10−3	2.89×10−10
IL-13 K105A	1.31×106	7.71×10−3	5.89×10−9	9.16×106	1.06×10−5	1.16×10−12
IL-13 F107A			>1.0×10−7*	1.15×107	9.45×10−4	8.91×10−11
IL-13 R108A			2.11×10−7
ITC Thermodynamics
Titrand	Titrant	ΔH (kcal/mol)	ΔS (cal/mol*K)	ΔG (kcal/mol)	KD (M−1)	n
IL-13	IL-13Rα1	−11.4	−2.8	−10.5	2.5×10−8	0.937
IL-13	IL-13Rα2	−20	N.D.	N.D.	N.D.	0.980
IL-13/ IL-13Rα1	IL-R13α2	−20.1	−14.5	−15.7	4.7×10−12	0.943
IL-13 K104A	IL-R13α2	−20.4	−28.2	−11.9	2.78×10−9	0.884
IL-13 F107A	IL-R13α2	−17.1	−15.7	−12.3	1.27×10−9	0.949

^*Accurate K_D could not be determined due to non-specific binding of IL-13F107A to the SPR control channel at concentrations >1 µM