Figure 9.

Model proposed for Ca²⁺/CaM-dependent regulation of 4.1G binding to membrane proteins. Erythroblast intracellular Ca²⁺ concentration is normally maintained at less than 0.1 μM (10⁻⁷ M) as described in Figure 7 [39, 40]. 4.1G binds to band 3, GPC and p55 with a K _(D) of 10⁻⁷ M. At higher Ca²⁺ concentrations, CaM binds to the HP region with a K _(D) of 10⁻⁸ M. This results in a conformational and/or electric surface change which alters 4.1G binding sites, 4.1G interacting consequently with lower affinity with its binding partners GPC and no longer interacting with band 3 and p55. This model implies a Ca²⁺/CaM-dependent regulation of 4.1G binding to transmembrane proteins.