Highly Anomalous Energetics of Protein Cold Denaturation Linked to Folding-Unfolding Kinetics
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AuthorRomero Romero, María Luisa; Inglés Prieto, Álvaro; Ibarra Molero, Beatriz; Sánchez Ruiz, José Manuel
Public Library of Science (PLOS)
CalorimetryChloridesCircular dichroism spectroscopyEnergetic materialsEnthalpyFree energyGuanidinesRelaxation (physics)
Romero Romero, M.L.; Inglés Prieto, A.; Ibarra Molero, B.; Sánchez Ruiz, J.M. Highly Anomalous Energetics of Protein Cold Denaturation Linked to Folding-Unfolding Kinetics. Plos One, 6(7): e23050 (2011). [http://hdl.handle.net/10481/31078]
SponsorshipThis work was supported by FEDER (“Fondo Europeo de DEsarrollo Regional”) funds and Grants BIO2009-09562 and CSD2009-00088 from the Spanish Ministry of Science and Innovation.
Despite several careful experimental analyses, it is not yet clear whether protein cold-denaturation is just a “mirror image” of heat denaturation or whether it shows unique structural and energetic features. Here we report that, for a well-characterized small protein, heat denaturation and cold denaturation show dramatically different experimental energetic patterns. Specifically, while heat denaturation is endothermic, the cold transition (studied in the folding direction) occurs with negligible heat effect, in a manner seemingly akin to a gradual, second-order-like transition. We show that this highly anomalous energetics is actually an apparent effect associated to a large folding/unfolding free energy barrier and that it ultimately reflects kinetic stability, a naturally-selected trait in many protein systems. Kinetics thus emerges as an important factor linked to differential features of cold denaturation. We speculate that kinetic stabilization against cold denaturation may play a role in cold adaptation of psychrophilic organisms. Furthermore, we suggest that folding-unfolding kinetics should be taken into account when analyzing in vitro cold-denaturation experiments, in particular those carried out in the absence of destabilizing conditions.