Cytosolic chaperonin CCT possesses GTPase activity

Susumu Noguchi,Sumio Watanabe,Yasushi Kawata,Ryoji Kobayashi,Soh Yamamoto,Toshio Miyazaki,Katsunori Imai,Haruki Senoo,Hiroshi Kubota,Mitsutoshi Jikei,Hideaki Itoh,Kazuyoshi Toyoshima,Michiro Otaka

doi:10.4236/ajmb.2011.13013

Abstract

Cytosolic chaperonin CCT (also known as TRiC) is a hetero-oligomeric cage-like molecular chaperone that assists in protein folding by ATPase cycle-dependent conformational changes. However, role of the nucleo-tide binding and hydrolysis in CCT-assisted protein folding is still poorly understood. We purified CCT by using ATP-Sepharose and other columns, and found that CCT possesses ability to hydrolyze GTP, with an activity level very similar to the ATPase activity. CCT was more resistant to proteinase K treatment in the presence of GTP or ATP. These results suggest that the GTPase activity of CCT may play a role in chaperone-assisted protein folding.

Highlights

Many cellular proteins require assistance with molecular chaperones to obtain functional conformations [1,2]
Chaperonins has been divided into two classes: group I chaperonins are found in prokaryotes and eukaryotic organelles including mitochondria and cytoplasm [4,5,6] whereas group II chaperonins are found in the eukaryotic cytosol and archaea [7,8]
Fractions containing chaperonin containing t-complex polypeptide 1 (CCT) were applied to a 10 ml ATP-Sepharose (Sigma, St Louis, MO, USA) column using buffer A supplemented with 5 mM MgCl2 and 1 mM CaCl2, and proteins were eluted with buffer A supplemented with 5 mM ATP and 10 mM EDTA

Summary

Introduction

Many cellular proteins require assistance with molecular chaperones to obtain functional conformations [1,2]. Chaperonins are large cylindrical complexes that enhance the efficiency of protein folding [3]. These complexes are two-ring assemblies that posses a central cavity to accommodate non-native proteins, and the substrate proteins are released after completion of folding. Group I chaperonins, includeing E. coli GroEL and mitochondrial HSP60, consist of 14 subunits and require ring-shaped cofactor GroES for their chaperone activities [3,9]. The group II chapronins have several characters distinct from the group I chaperonins: the former consists of 16 or 18 subunits and uses a built-in lid called helical protrusion to close the cylindrical structure [8,10]

Methods

Results

Conclusion