Capping protein dynamics are defined by the stalk and restricted by CPI-motif and V-1 binding

Actin capping protein (CP) controls actin filament growth by capping the filament barbed end and preventing it from gaining and losing subunits. Proper regulation of barbed-end capping is essential for controlling actin polymerization processes that underlie cell shape and cell motility. In vertebrates, V-1 (myotrophin) and various CP-interacting motif (CPI-motif) proteins bind CP and regulate barbed-end capping both sterically and allosterically. The effect of V-1 and CPI-motif binding has been well studied, but a critical gap exists in understanding the dynamics of apo CP. Here, we employ molecular dynamics simulations and Markov state modeling to map the conformational landscape of apo CP, identifying at least five stable and metastable states. Principal component analysis indicates that the stalk is the main driver of CP dynamics, with stalk twisting and tilting defining the apo states. We find that V-1 and CPI-motif binding limit CP dynamics, restricting the stalk to similar yet distinct twist and tilt angles. Lastly, we find that yeast CP exhibits a much more confined conformational landscape, hinting at species-specific CP dynamics. Collectively, this work improves our understanding of apo CP and its ligand-induced conformational shifts and provides a molecular basis for studying allosteric linkage between the capping interface and the stalk.