Mechanical Response of the Coiled Coil

Abstract

First discovered by Crick, coiled coils are a prevalent ropelike protein motif formed by two or more α-helices. Coiled coils are found in many functionally diverse protein complexes, some of which are involved in gene regulation, muscle contraction and cell signaling. Since they undergo functional bending, twisting, buckling and stretching motions, understanding the mechanical response of coiled coils is crucial for describing the conformational states of these proteins. The energetic of a coiled coil involves a competition between elastic deformation and hydrophobic interaction of residues of each helix. In this work, we present an energetic and geometric investigation of coiled coils using a coarse-grained elastic model. In this model, we treat α-helices as elastic rods where each rod interacts with another exclusively through beads representing the hydrophobic residues. One interesting result is that our model estimates the persistence length of a coiled coil dimer as 165 nm which is less than twice the persistence length of a single α-helix. We have validated our results using steered molecular dynamics simulations and we discuss our results and possible applications of the model to higher level complexes.