Connecting Protein Millisecond Conformational Dynamics to Protein Thermal Stability.

The stability of protein folded states is crucial for its function, yet the relationship with the protein sequence remains poorly understood. Prior studies have focused on the amino acid composition and thermodynamic couplings within a single folded conformation, overlooking the potential contribution of protein dynamics. Here, we address this gap by systematically analyzing the impact of alanine mutations in the C-terminal β-strand (β5) of ubiquitin, a model protein exhibiting millisecond timescale interconversion between two conformational states differing in the β5 position. Our findings unveil a negative correlation between millisecond dynamics and thermal stability, with alanine substitutions at seemingly flexible C-terminal residues significantly enhancing thermostability. Integrating spectroscopic and computational approaches, we demonstrate that the thermally unfolded state retains a substantial secondary structure but lacks β5 engagement, recapitulating the transition state for millisecond dynamics. Thus, alanine mutations that modulate the stabilities of the folded states with respect to the partially unfolded state impact both the dynamics and stability. Our findings underscore the importance of conformational dynamics with implications for protein engineering and design.