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Figure 6.
Figure 6. Structure-based GroEL-assisted protein folding
pathways. The affinity of GroEL for protein substrate at the
apical domain and ATP at the equatorial is labeled as H for high
and L for low; the underlined labels are asymmetric within each
ring and the lowercase indicates the process of switching.
Dashed and dotted arrows are minor alternative pathways. The
lower pathway is for large protein substrates that cannot be
encapsulated inside the GroEL/GroES cavity. The upper pathway is
for small protein substrates that can be encapsulated. A minor
upper pathway includes the migration of bound ATP from the
trans-ring to the cis-ring, before the formation of the
asymmetric GroEL/GroES complex. The formation of the GroEL/GroES
complex always requires the binding of ATP in the cis-ring. ATP
hydrolysis leads to the dead-end GroEL/ES asymmetric complex,
which can only be disassembled by the binding of ATP in the low
affinity sites of the trans-ring. The symmetric
(GroES)[7](GroEL)[14](GroES)[7] complex, which has been observed
under the physiological conditions,[8., 9., 10. and 11.] is not
included in the diagram, because it has no accessible binding
sites for the protein substrates and may represent a storage
form for the excess chaperonins.
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