Chaperonin—Co-chaperonin Interactions - The Networking of Chaperones by Co-chaperones - page 158

Fig. 8.3 Structure of GroES. Side view of GroES heptameric structure, as it occurs bound to
GroEL and ATP, showing the flexible loops that interact with GroEL pointing downwards ( a ). The
backbone structure of the GroES monomer interacting with the top of the apical domain of GroEL
( b ). Alpha helices are shown in red and ʲ-sheets in yellow . The images were generated using
PyMol (DeLano Scientific) from coordinates in PDB: 1AON
Coalescence of the disordered and flexible C-terminal segments of the subunits in
each ring blocks the central channel at the equatorial domain causing discontinuity
between the cavities turning them into two separate chambers for folding (Chen
et al. 1994 ). Specific hydrophilic amino acid residues in the C-terminal region were
identified as being vital in maintaining an appropriate environment for protein fold-
ing within the central cavity of GroEL (Machida et al. 2009 ).
GroES is composed of seven identical 10 kDa subunits that form a lid-like struc-
ture (Hunt et al. 1996 ; Mande et al. 1996 ). These subunits form an irregular ʲ-barrel
structure formed by five ʲ-strands with anti-parallel pairing of the last ʲ-strand of
one subunit with the first ʲ-strand of the following subunit (Landry et al. 1993 ).
Each subunit includes two loop regions, one facing upwards that forms the roof
of the lid and one extending downwards from the bottom of the lid that consti-
tutes a highly flexible mobile loop 16 amino acids in length (Fig. 8.3 ; Landry et al.
1993 ). Binding of GroES to GroEL is mediated by the seven flexible loops which
are induced to form a ʲ-hairpin structure upon formation of the GroEL/GroES/
ATP complex (Fig. 8.3 ; Richardson et al. 2001 ). Mutations in the mobile loop dis-
rupted GroES binding to GroEL (Zeilstra-Ryalls et al. 1994 ). The contribution of
the mobile loop was studied using a synthetic peptide resembling the loop, which
lacked structure until induced to form the ʲ-hairpin structure when bound to GroEL