The conformational equilibrium of human growth hormone

Marina R. Kasimova, Sam J. Milstein, Ernesto Freire

Research output: Contribution to journalArticle

Abstract

The structural stability of recombinant human growth hormone (rhGH) has been studied by differential scanning calorimetry, circular dichroism and by following the tyrosine and histidine chemical shifts in the 1H NMR spectrum. These studies demonstrate that the folding/unfolding equilibrium of rhGH involves a partially folded dimeric intermediate. The formation of this dimeric intermediate is a reversible process. At acid pH (pH 3) the conformational equilibrium is reversible even at high protein concentrations (10 mg/ml). At neutral pH reversibility is observed only at low protein concentrations (< 0.5 mg/ml). The free energy of this intermediate conformation is only ~ 3 kcal/mol apart from the native state indicating that the conformational equilibrium can be effectively modulated by changes in solvent composition or physical conditions. According to the spectroscopic and thermodynamic results, the formation of the dimeric intermediate occurs without a major loss in helical content and is driven by the formation of substantial hydrophobic contacts between two partially folded molecules. A thermodynamic model that accounts quantitatively for the experimental data has been developed. These studies demonstrate that partially folded conformations of certain proteins are able to form stoichiometric complexes, and that the formation of these complexes provide a significant source of stabilizing Gibbs energy for conformational states that, otherwise, will be characterized by extremely unfavorable free energies.

Original languageEnglish (US)
Pages (from-to)409-418
Number of pages10
JournalJournal of molecular biology
Volume277
Issue number2
DOIs
StatePublished - Mar 27 1998
Externally publishedYes

Keywords

  • Calorimetry
  • Folding intermediates
  • Human growth hormone
  • Protein stability
  • Thermodynamics

ASJC Scopus subject areas

  • Structural Biology
  • Molecular Biology

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