title: Assisted protein folding at low temperature: evolutionary adaptation of the Antarctic fish chaperonin CCT and its client proteins.
abstract: Eukaryotic ectotherms of the Southern Ocean face energetic challenges to protein folding assisted by the cytosolic chaperonin CCT. We hypothesize that CCT and its client proteins (CPs) have co-evolved molecular adaptations that facilitate CCT-CP interaction and the ATP-driven folding cycle at low temperature. To test this hypothesis, we compared the functional and structural properties of CCT-CP systems from testis tissues of an Antarctic fish, Gobionotothen gibberifrons (Lönnberg) (habitat/body T = -1.9 to +2°C), and of the cow (body T = 37°C). We examined the temperature dependence of the binding of denatured CPs (β-actin, β-tubulin) by fish and bovine CCTs, both in homologous and heterologous combinations and at temperatures between -4°C and 20°C, in a buffer conducive to binding of the denatured CP to the open conformation of CCT. In homologous combination, the percentage of G. gibberifrons CCT bound to CP declined linearly with increasing temperature, whereas the converse was true for bovine CCT. Binding of CCT to heterologous CPs was low, irrespective of temperature. When reactions were supplemented with ATP, G. gibberifrons CCT catalyzed the folding and release of actin at 2°C. The ATPase activity of apo-CCT from G. gibberifrons at 4°C was ∼2.5-fold greater than that of apo-bovine CCT, whereas equivalent activities were observed at 20°C. Based on these results, we conclude that the catalytic folding cycle of CCT from Antarctic fishes is partially compensated at their habitat temperature, probably by means of enhanced CP-binding affinity and increased flexibility of the CCT subunits.
authors.affiliation: Centro Nacional de Biotechnología (CNB-CSIC), Campus de la Universidad Autónoma de Madrid, 28049 Madrid, Spain.
authors.forename: Jorge
authors.initials: J
authors.lastname: Cuellar
authors.forename: Hugo
authors.initials: H
authors.lastname: Yébenes
authors.forename: Sandra K
authors.initials: SK
authors.lastname: Parker
authors.forename: Gerardo
authors.initials: G
authors.lastname: Carranza
authors.forename: Marina
authors.initials: M
authors.lastname: Serna
authors.forename: José María
authors.initials: JM
authors.lastname: Valpuesta
authors.forename: Juan Carlos
authors.initials: JC
authors.lastname: Zabala
authors.forename: H William
authors.initials: HW
authors.lastname: Detrich
keywords: Actin; CCT; Chaperone; Chaperonin; Evolution; Protein folding; Thermal adaptation; TriC; Tubulin