On the distribution of ligands within the asymmetric chaperonin complex, GroEL14.ADP7.GroES7.
In the presence of MgATP or MgADP the E. coli chaperonin proteins, GroEL and GroES, form a stable asymmetric complex with a stoichiometry of two GroEL7:one GroES7: seven MgADP. The distribution of the ligands between the two heptameric GroEL rings is crucial to our understanding of the mechanism of chaperonin-assisted folding, being either cis (i.e. [GroEL7.MgADP7.GroES7]-[GroEL7]) or trans (i.e. [GroEL7.MgADP7]-[GroEL7.GroES7]. On the basis of cross-linking experiments with 8-azido-ATP and the heterobifunctional reagent, N-succinimidyl 3-(2-pyridyldithio) propionate (SPDP), it was suggested that GroES and MgADP are bound to the same GroEL ring which resists proteinase K digestion [Nature 366 (1993) 228-233]. However, we find that the SPDP-promoted cross linking of GroES and GroEL occurs in the absence of Mg2+, ADP or ATP, which are required for the formation of the asymmetric complex. Cross-linking is shown to occur only when the SPDP-modified GroES is co-precipitated with GroEL by trichloracetic acid. Furthermore, there are structural grounds for questioning whether SPDP can crosslink, in a physiologically relevant manner, an amino group of GroES with any of the cysteinyl groups of GroEL.
Girshovich
A S
AS
Department of Biochemistry, Weizmann Institute of Science, Rehovot, Israel.
Bochkareva
E S
ES
Todd
M J
MJ
Lorimer
G H
GH
D000244:Adenosine Diphosphate / Q000378:metabolism*; D001665:Binding Sites; D018835:Chaperonin 10 / Q000378:metabolism*; D018834:Chaperonin 60 / Q000737:chemistry / Q000378:metabolism*; D003432:Cross-Linking Reagents; D003545:Cysteine / Q000737:chemistry; D004926:Escherichia coli / Q000378:metabolism; D008024:Ligands; D046911:Macromolecular Substances; D008958:Models, Molecular; D011487:Protein Conformation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D013388:Succinimides
D018835:Chaperonin 10; D018834:Chaperonin 60; D003432:Cross-Linking Reagents; D008024:Ligands; D046911:Macromolecular Substances; D013388:Succinimides; C018151:N-succinimidyl 3-(2-pyridyldithio)propionate; D000244:Adenosine Diphosphate; D003545:Cysteine