Chaperonin—Co-chaperonin Interactions - The Networking of Chaperones by Co-chaperones - page 157

et al. 2006 ) and cryo-electron microscopy structures (Ranson et al. 2006 ; Chen et al.
2006 ). Co-chaperonin structures alone have been reported for GroES (Boudker
et al. 1997 ; Hunt et al. 1996 ; Seale et al. 1996 ).
The ability of GroEL and GroES to enhance protein folding is embedded in the
unique quaternary structures of these proteins (Fig. 8.1a ). The arrangement of the
GroEL subunits results in an oligomeric structure consisting of fourteen subunits
arranged in two inverted rings, while the GroES subunits are arranged into a single
ring of seven subunits, and both structures display seven-fold rotationally symmet-
ric ring-shaped oligomers (Fig. 8.1b ). The GroEL subunits are composed mainly
of α-helices and the arrangement of the subunits into two stacked GroEL rings cre-
ate a central channel that is split into two functionally separate cavities at the ring
interface (Braig et al. 1994 ; Braig et al. 1993 ). Each subunit is divided into three
distinct domains (Fig. 8.2 ): an ATP-binding equatorial domain that mediates inter-
actions between subunits of each ring, a substrate-binding apical domain including
co-chaperone binding sites, and an intermediate domain that connects both domains
and transmits conformational changes generated by nucleotide binding between the
equatorial and apical domains (Braig et al. 1994 ; Fenton et al. 1994 ). The apical
domains are positioned on the outside of each ring, the intermediate domains are in
the middle and the equatorial domains are positioned at the interface of both rings.
Fig. 8.2 Binding of GroES induces a large conformational change in GroEL. Each subunit of
GroEL is divided into three distinct domains: an apical domain, an equatorial domain and an
intermediate domain that connects both domains. Unbound GroEL ( a ) undergoes large rigid body
movements of the apical domain upon binding of GroES ( b ). Apical domain is twisted 90ﾰ relative
to the open ring not bound to GroES. Alpha helices are shown in red and ʲ-sheets in yellow . The
images were generated using PyMol (DeLano Scientific) from coordinates in PDB: 1AON