Exposure of hydrophobic surfaces on the chaperonin GroEL oligomer by protonation or modification of His-401

Don L. Gibbons, Paul M. Horowitz

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24 Scopus citations


Hydrophobic exposure on the chaperonin GroEL is increased 6-10-fold after the protein is treated with the His-reactive reagent diethyl pyrocarbonate (DEP), or the solution pH is lowered to 5.5. The induced hydrophobic surfaces have the same 1,1'-bis(4-anilino)naphthalene-5,5'-disulfonic acid (bis-ANS) binding characteristics as unperturbed GroEL: a K(d) ≃ 3.5 μM, a maximum intensity at ~500 nm, and an average fluorescence lifetime of ~8.0 ns. The pK(a) for the pH-induced transition is 6.6, most likely attributable to the only histidine in GroEL, His-401, located in the intermediate domain. The modification of one histidine residue per monomer upon DEP treatment is supported by the correlation between the change in the absorbance at 242 nm for the N-carbethoxyhistidyl derivative and the increase in bis-ANS fluorescence. GroEL at pH 5.5 is tetradecameric and can capture urea- denatured rhodanese and release it as active enzyme. The GroEL-rhodanese complex is more stable to dissociation by 2.25 M urea than the complex formed at pH 7.8. We propose that His-401 is in a conformationally sensitive region such that protonation or modification can lead to increased exposure of hydrophobic surfaces capable of binding folding intermediates.

Original languageEnglish (US)
Pages (from-to)7335-7340
Number of pages6
JournalJournal of Biological Chemistry
Issue number13
StatePublished - Mar 31 1995
Externally publishedYes

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology


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