The Effects of Macromolecular Crowding on Calmodulin Structure and Function.

Macromolecular crowding and confinement are two factors that potentially affect protein structure and function in a complex cellular environment. The confinement effect on the structure and function of holoCaM [Ca2+ -loaded calmodulin (CaM)], a two-domain protein involved in many calcium-mediated signaling pathways, has been investigated previously. However, little is known about how macromolecular crowding affects holoCaM structure and function. Here, the structure-function correlations of holoCaM are investigated in macromolecular crowded environments. It was found that macromolecular crowding impacts its structure and function mildly. The major conformational states are still extended conformation with inter-domain separation in crowded environment as well as those in dilute solution, but the population of transiently compact conformation increases compared to dilute solution. Furthermore, macromolecular crowding facilitates the binding of CaM with AcN19 peptide (CaM-bind domain of α-syn). This study provides a direct comparison for macromolecular crowding and confinement effects on protein structure and function, which helps to understand chemistry regulation in living cells.