Abstract

Protein dynamics are influenced by solvent friction, due to the collisions of the sorrounding water molecules. However, another type of friction, emerging from the interactions of the polypeptide chain with itself, has also been found to be prevalent in protein and peptide folding, unfolded state dynamics and disordered proteins. However a clear molecular interpretation of this phenomenon is still missing. Here we examine this contribution using atomistic molecular dynamics simulations of several small proteins and peptides and model systems. We find that the experimental signatures usually attributed to internal friction can emerge from the features of protein energy landscapes. In particular the crossing of sharp torsional barriers, which are ubiquitous in protein conformational transitions, are sufficient to explain the anomalous viscosity dependence observed in experiments for many different systems, without the need to invoke an “internal” frictional effect.