a, Macroscopic thermodynamic cycle for CaM, Ca2+ and CaV1.2 IQ domain. K1 and K4 describe Ca2+ binding to CaM and the CaM/IQ complex, respectively. K2 and K3 describe IQ domain binding to calcium-free CaM and Ca2+
4:CaM, respectively. b, Calculated fraction of Ca2+
4:CaM as a function of Ca2+ concentration for CaM alone (red) or bound to the IQ domain (black curve). a, Macroscopic thermodynamic cycle for CaBP1, Ca2+ and CaV1.2 IQ domain. K1 and K4 describe Ca2+ binding to CaBP1 and the CaBP1/IQ complex, respectively. K2 and K3 describe IQ domain binding to calcium-free CaBP1 and Ca2+
2:CaBP1, respectively. d, Calculated fraction of Ca2+
2:CaBP1as a function of Ca2+ concentration for CaBP1 alone (orange) or bound to the IQ domain (grey curve).