The Effect of Macromolecular Crowding, Ionic Strength and Calcium Binding on Calmodulin Dynamics

TL;DR

This study combines computational and experimental methods to explore how cellular-like conditions such as crowding, ionic strength, and calcium binding influence calmodulin's structure and its ability to recognize targets.

Contribution

It introduces a multiscale computational approach to model calmodulin's charge distribution and structural changes under cellular conditions, linking these to functional implications.

Findings

Macromolecular crowding affects calmodulin conformation and helicity.

Calcium binding and ionic strength modulate EF hand orientation.

Structural changes influence calmodulin's target recognition specificity.

Abstract

The flexibility in the structure of calmodulin (CaM) allows its binding to over 300 target proteins in the cell. To investigate the structure-function relationship of CaM, we combined methods of computer simulation and experiments based on circular dichroism (CD) to investigate the structural characteristics of CaM that influence its target recognition in crowded cell-like conditions. We developed a unique multiscale solution of charges computed from quantum chemistry, together with protein reconstruction, coarse-grained molecular simulations, and statistical physics, to represent the charge distribution in the transition from apoCaM to holoCaM upon calcium binding. Computationally, we found that increased levels of macromolecular crowding, in addition to calcium binding and ionic strength typical of that found inside cells, can impact the conformation, helicity and the EF hand orientation of CaM. Because EF hand orientation impacts the affinity of calcium binding and the specificity of CaM's target selection, our results may provide unique insight into understanding the promiscuous behavior of calmodulin in target selection inside cells.