φ-Value Analysis for Ultrafast Folding Proteins by NMR Relaxation Dispersion

摘要

Proteins that fold rapidly, on the (sub-) microsecond time scale, offer the exciting prospect of direct comparison between experimental data and molecular dynamics simulations. The standard method for assessing the role of amino acid side chains in the transition state for folding is a protein engineering approach commonly referred to as φ-value analysis (Figure S1, Supporting Information, SI). Application of φ-value analysis to ultrafast folding proteins is stymied by several technical difficulties: (i) folding rates are too fast for conventional stopped-flow methods, (if) suitable spectroscopic probes often are not available in natural amino acid sequences, and (iii) mutational effects on the denatured state ensemble obscure the interpretation of φ-values.