Protein denaturation at a single-molecule level: the effect of nonpolar environments and its implications on the unfolding mechanism by proteasesElectronic supplementary information (ESI) available: The schematic diagram of environment change, the comparison of F-E curves obtained at various stretching velocities, the details of the QM-WLC model and the process of generation of fitting curves, the comparison of F-E curves of polylysine obtained in PBS and I278 obtained in 6 M GdnHCl, the normali

• Main Authors: Cheng, Bo, Wu, Shaogui, Liu, Shixin, Rodriguez-Aliaga, Piere, Yu, Jin, Cui, Shuxun
• Format: Article
• Language: English
• ISSN: 2040-3364; 2040-3372
• DOI: 10.1039/c4nr07140a

Most proteins are typically folded into predetermined three-dimensional structures in the aqueous cellular environment. However, proteins can be exposed to a nonpolar environment under certain conditions, such as inside the central cavity of chaperones and unfoldases during protein degradation. It remains unclear how folded proteins behave when moved from an aqueous solvent to a nonpolar one. Here, we employed single-molecule atomic force microscopy and molecular dynamics (MD) simulations to investigate the structural and mechanical variations of a polyprotein, I27 8 , during the change from a polar to a nonpolar environment. We found that the polyprotein was unfolded into an unstructured polypeptide spontaneously when pulled into nonpolar solvents. This finding was corroborated by MD simulations where I27 was dragged from water into a nonpolar solvent, revealing details of the unfolding process at the water/nonpolar solvent interface. These results highlight the importance of water in maintaining folding stability, and provide insights into the response of folded proteins to local hydrophobic environments. When pulled into a nonpolar solvent by AFM, the single molecule of a polyprotein will be denatured into an unstructured polypeptide spontaneously.