Assisted protein folding at low temperature: evolutionary adaptation of the Antarctic fish chaperonin CCT and its client proteins

Jorge Cuellar,Gerardo Carranza,Marina Serna,Juan Carlos Zabala,H William Detrich,Sandra K Parker,José María Valpuesta,Hugo Yébenes

doi:10.1242/bio.20147427

Abstract

ABSTRACTEukaryotic 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.

Highlights

Protein quality control and maintenance of the proteome are essential for the health of cells and organisms (Hartl et al, 2011)
The chaperonin containing t-complex polypeptide-1 [CCT, aka TCP-1 ring complex (TriC)] plays a central role in cellular homeostasis by assisting the folding of,10% of newly synthesized proteins, including tubulins and actins (‘‘client proteins’’ or CPs) (Thulasiraman et al, 1999; Valpuesta et al, 2002; Dekker et al, 2008; Yam et al, 2008; Valpuesta et al, 2005)
We suggest that adaptation of the function of Antarctic fish CCT at low temperature is based on lowering the activation energy barrier(s) of the folding cycle through enhanced CP-binding affinity and increased subunit flexibility

Summary

Introduction

Protein quality control and maintenance of the proteome are essential for the health of cells and organisms (Hartl et al, 2011). The chaperonin containing t-complex polypeptide-1 [CCT, aka TCP-1 ring complex (TriC)] plays a central role in cellular homeostasis by assisting the folding of ,10% of newly synthesized proteins, including tubulins and actins (‘‘client proteins’’ or CPs) (Thulasiraman et al, 1999; Valpuesta et al, 2002; Dekker et al, 2008; Yam et al, 2008; Valpuesta et al, 2005). CCT is a cylindrical, 16-subunit toroid composed of eight distinct subunits (CCTa–CCTh) that form two eight subunit, back-to-back rings, each containing a folding ‘‘cage’’ for CPs (Yebenes et al, 2011; Leitner et al, 2012). Additional protein co-factors are required either to deliver CPs to CCT or to facilitate final maturation and oligomerization of CPs after their interactions with CCT (Valpuesta et al, 2002; Valpuesta et al, 2005; Yebenes et al, 2011)

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