The role of topology on protein thermal stability

TL;DR

This study uses Monte Carlo simulations to investigate how protein topology, specifically knots, influences thermal stability, revealing that knotting does not affect melting temperature and explaining discrepancies in experimental results.

Contribution

The paper demonstrates through simulations that protein knotting does not impact thermal stability, clarifying conflicting experimental and computational findings.

Findings

Tm is independent of protein knotting.

Timescale separation affects observed thermal stability.

Experimental Tm may reflect non-equilibrium states.

Abstract

For several decades, experimental and computational studies have been used to investigate the potential functional role of knots in protein structures. A property that has attracted considerable attention is thermal stability, i.e., the extent to which a protein retains its native conformation and biological activity at high temperatures, without undergoing denaturation or aggregation. Thermal stability is quantified by the melting temperature Tm, an equilibrium property that corresponds to the peak of heat capacity in differential scanning calorimetry (DSC) experiments. Experimental and computational studies report conflicting effects of knotting on protein thermal stability. Here, we use extensive Monte Carlo simulations of a simple C-alpha model of protein YibK, with energetics modeled by the Go potential, to show that Tm does not depend on the topological state of the protein. Our simulations further support the view that the discrepancy between the experimental and computational results stems from a pronounced separation of timescales for unknotting and unfolding that is inherent to deeply knotted proteins like YibK. In particular, the timescale separation implies that the complete unfolding-untying transition may not be accessible within the duration of a DSC experiment, whose apparent Tm measurements likely reflect a non-equilibrium distribution lacking unfolded states that are also unknotted.