The energy cost of polypeptide knot formation and its folding consequences

• Published in: Nature communications Vol. 8; no. 1; pp. 1581 - 8
• Main Authors: Bustamante, Andrés, Sotelo-Campos, Juan, Guerra, Daniel G., Floor, Martin, Wilson, Christian A. M., Bustamante, Carlos, Báez, Mauricio
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 17.11.2017; Nature Publishing Group; Nature Portfolio
• Subjects: 631/45/470; 631/57/2265; 631/57/2266; Chains; Folding; Free energy; Humanities and Social Sciences; Kinetics; Knots; multidisciplinary; Polypeptides; Protein folding; Proteins; Residues; Science; Science & Technology - Other Topics; Science (multidisciplinary)
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-017-01691-1

Knots are natural topologies of chains. Yet, little is known about spontaneous knot formation in a polypeptide chain—an event that can potentially impair its folding—and about the effect of a knot on the stability and folding kinetics of a protein. Here we used optical tweezers to show that the free energy cost to form a trefoil knot in the denatured state of a polypeptide chain of 120 residues is 5.8 ± 1 kcal mol −1 . Monte Carlo dynamics of random chains predict this value, indicating that the free energy cost of knot formation is of entropic origin. This cost is predicted to remain above 3 kcal mol −1 for denatured proteins as large as 900 residues. Therefore, we conclude that naturally knotted proteins cannot attain their knot randomly in the unfolded state but must pay the cost of knotting through contacts along their folding landscape. The effect of knots on protein stability and folding kinetics is not well understood. Here the authors combine optical tweezer experiments and calculations to experimentally determine the energy cost for knot formation, which indicates that knotted proteins evolved specific folding pathways because knot formation in unfolded chains is unfavorable.