Table S1. Surface plasmon resonance derived binding kinetics.

Sample	ka (107/Ms)	kd (10−2/s)	KD (nM)
hTG2 GDP	0.60 ± 0.05	2.74 ± 0.29	4.56 ± 0.10
hTG2 DP3-3/Ca2+	0.10 ± 0.013	3.01 ± 0.18	3.07 ± 0.20
mTG2 GDP	0.14 ± 0.00	0.44 ± 0.01	3.21 ± 0.06
mTG2 DP3-3/Ca2+	0.10 ± 0.00	0.67 ± 0.01	6.44 ± 0.14

Data are presented as the means ± SD. Based on two experiments. GDP-bound TG2: TG2 bound to GDP, closed conformation, presumably representing intracellular TG2; DP3-3/Ca²⁺ bound TG2: TG2 with irreversible active site inhibitor in presence of Ca²⁺, open conformation, as expected to occur extracellularly due to the high extracellular concentration of Ca²⁺. k_a, association rate constant; k_d, dissociation rate constant.