Thermal and mechanical multistate folding of ribonuclease H

Two different classes of experimental techniques exist by which protein folding mechanisms are ascertained. The first class, of which circular dichroism is an example, probes thermally-induced folding. The second class, which includes atomic force microscopy and optical tweezers, measures mechanically-induced folding. In this article, we investigate if proteins fold/unfold via the same mechanisms both thermally and mechanically. We do so using Ribonuclease H, a protein that has been shown to fold through a three-state mechanism using both types of experimental techniques. A detailed, molecular-level description of the states involved in thermal and mechanical folding shows that mechanisms for both types are globally similar, but small difference exist in the most unfolded conformations. Comparison to previous work suggests a universal folding behavior for proteins with a core helical bundle.