title: Unstructured intermediate states in single protein force experiments.
abstract: Recent single-molecule force measurements on single-domain proteins have highlighted a three-state folding mechanism where a stabilized intermediate state (I) is observed on the folding trajectory between the stretched state and the native state. Here we investigate on-lattice protein-like heteropolymer models that lead to a three-state mechanism and show that force experiments can be useful to determine the structure of I. We have mostly found that I is composed of a core stabilized by a high number of native contacts, plus an unstructured extended chain. The lifetime of I is shown to be sensitive to modifications of the protein that spoil the core. We then propose three types of modifications--point mutations, cuts, and circular permutations--aiming at: (1) confirming the presence of the core and (2) determining its location, within one amino acid accuracy, along the polypeptide chain. We also propose force jump protocols aiming to probe the on/off-pathway nature of I.
authors.affiliation: Departament de Física Fonamental, Facultat de Física, Universitat de Barcelona, Diagonal 647, Barcelona 08028, Spain.
authors.forename: Ivan
authors.initials: I
authors.lastname: Junier
authors.forename: Felix
authors.initials: F
authors.lastname: Ritort
mesh_terms: D019943:Amino Acid Substitution / Q000235:genetics; D008958:Models, Molecular; D009010:Monte Carlo Method; D010455:Peptides / Q000737:chemistry; D017354:Point Mutation; D011108:Polymers / Q000737:chemistry; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D016914:Ribonuclease H / Q000737:chemistry; D013816:Thermodynamics
chemical_list: D010455:Peptides; D011108:Polymers; D016914:Ribonuclease H