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Chaperonin‐assisted folding of glutamine synthetase under nonpermissive conditions: Off‐pathway aggregation propensity does not determine the co‐chaperonin requirement
Author(s) -
Voziyan Paul A.,
Fisher Mark T.
Publication year - 2000
Publication title -
protein science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.353
H-Index - 175
eISSN - 1469-896X
pISSN - 0961-8368
DOI - 10.1110/ps.9.12.2405
Subject(s) - groel , groes , chaperonin , protein folding , chemistry , biochemistry , biophysics , chaperone (clinical) , antiparallel (mathematics) , monomer , folding (dsp implementation) , biology , escherichia coli , organic chemistry , medicine , physics , pathology , quantum mechanics , magnetic field , electrical engineering , gene , engineering , polymer
One of the proposed roles of the GroEL‐GroES cavity is to provide an “infinite dilution” folding chamber where protein substrate can fold avoiding deleterious off‐pathway aggregation. Support for this hypothesis has been strengthened by a number of studies that demonstrated a mandatory GroES requirement under nonpermissive solution conditions, i.e., the conditions where proteins cannot spontaneously fold. We have found that the refolding of glutamine synthetase (GS) does not follow this pattern. In the presence of natural osmolytes trimethylamine N‐oxide (TMAO) or potassium glutamate, refolding GS monomers readily aggregate into very large inactive complexes and fail to reactivate even at low protein concentration. Surprisingly, under these “nonpermissive” folding conditions, GS can reactivate with GroEL and ATP alone and does not require the encapsulation by GroES. In contrast, the chaperonin dependent reactivation of GS under another nonpermissive condition of low Mg 2+ (<2 mM MgCl 2 ) shows an absolute requirement of GroES. High‐performance liquid chromatography gel filtration analysis and irreversible misfolding kinetics show that a major species of the GS folding intermediates, generated under these “low Mg 2+ ” conditions exist as long‐lived metastable monomers that can be reactivated after a significantly delayed addition of the GroEL. Our results indicate that the GroES requirement for refolding of GS is not simply dictated by the aggregation propensity of this protein substrate. Our data also suggest that the GroEL‐GroES encapsulated environment is not required under all nonpermissive folding conditions.