Chaperonin—Co-chaperonin Interactions - The Networking of Chaperones by Co-chaperones - page 153

Fig. 8.1 Structure of the GroEL/GroES complex. The GroEL/GroES complex comprises of two
heptameric rings of GroEL stacked back-to-back with the GroES 'lid' bound to the cis ring to
form a barrel-shaped complex, showing the side ( a ) and the top ( b ) views of the complex. Alpha
helices are shown in red and ʲ-sheets in yellow . The images were generated using PyMol (DeLano
Scientific) from coordinates in PDB: 1AON
domain and are then dislodged and driven into the cavity by the binding of the co-
chaperonin to the same area (Hartl and Hayer-Hartl 2002 ). The folding process is
driven by the binding and hydrolysis of ATP which triggers a complex set of alloste-
ric signals both within and between the stacked rings (Gray and Fersht 1991 ; Todd
et al. 1993 ). GroEL is critical for the correct folding of many proteins in the cell,
under both normal and stress conditions. The folding of nascent polypeptides often
requires the cooperation of both the Hsp70 and Hsp60 families and these families
are also responsible for most of the general folding events in the cell (Hartl et al.
1992 ; Fink 1999 ). While CCT is not upregulated during heat shock (Horwich et al.
2007 ), GroEL and mitochondrial Hsp60 are heat inducible. In addition to ensuring
the correct folding of proteins, chaperonins play a role in the assembly of protein
complexes (Seo et al. 2010 ) and trafficking of proteins (Xu et al. 2011 ).
The Gp31 protein from bacteriophage T4, a functional co-chaperonin that pro-
motes the assembly of the T4 major capsid protein, can functionally substitute for
GroES resulting in an increase in size and hydrophilicity of the enclosed chamber
(van der Vies et al. 1994 ; Hunt et al. 1997 ). Another co-chaperonin from bacterio-
phage RB49 called CocO is distantly related to GroES (Ang et al. 2001 ). Both of
these bacteriophage co-chaperonins utilize host encoded GroEL to assemble capsid
proteins and both proteins could functionally replace GroES in E. coli (Keppel et al.
2002 ). Interestingly, the first viral-encoded chaperonin was identified in the genome
of Pseudomonas aeruginosa bacteriophage EL (Hertveldt et al. 2005 ), and later
demonstrated to have functional properties similar to GroEL except that it does not
require a co-chaperonin for activity (Kurochkina et al. 2012 ). A wide range of newly
identified functions have been attributed to eukaryotic Hsp60, including roles in
carcinogenesis, immunity and cell signalling (reviewed by (Calderwood et al. 2007 ;