GroEL is a cylinder of two seven-subunit rings. Hydrophobic surfaces inside one ring bind a protein that has not folded. ATP and the lid protein GroES then close a chamber around the protein. The protein folds alone in that chamber, safe from aggregation. ATP hydrolysis then opens the lid again.
14 GroEL + 7 GroES
Two rings of seven GroEL subunits, capped by one GroES ring.
~60 kDa
Denatured proteins smaller than the 57 kDa GroEL subunit stay inside the closed cage. An 82 kDa protein binds GroEL but never enters.
7 ATP
One ring binds and hydrolyses seven ATP per cycle.
0.12 s^-1 per subunit
Rate of the hydrolysis step after GroES binds. A later study with another method found a faster burst, about 0.5 s^-1 (Ye and Lorimer 2013).
0.042 s^-1 per subunit
GroES leaves at the steady-state hydrolysis rate, so without substrate the lid stays on for about 24 s. A FRET assay gave 0.031 s^-1 (Rye et al. 1999).
~1 s
GroES residence time with substrate
17Substrate protein speeds the exchange of GroES and nucleotide.
about twice the open-ring volume
Cis cavity volume on GroES binding
2Elevation and twist of the apical domains double the central cavity.
~85 proteins
Obligate substrates in E. coli
13About 250 proteins bind GroEL; about 85 need it to reach the native state.