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High pressure NMR reveals that apomyoglobin is an equilibrium mixture from the native to the unfolded

Academic Article
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Overview

authors

  • Kitahara, R.
  • Yamada, H.
  • Akasaka, K.
  • Wright, Peter

publication date

  • July 2002

journal

  • Journal of Molecular Biology  Journal

abstract

  • Pressure-induced reversible conformational changes of sperm whale apomyoglobin have been studied between 30 bar and 3000 bar on individual residue basis by utilizing 1H/15N hetero nuclear single-quantum coherence two-dimensional NMR spectroscopy at pH 6.0 and 35 degrees C. Apomyoglobin showed a series of pressure-dependent NMR spectra as a function of pressure, assignable to the native (N), intermediates (I), molten globule (MG) and unfolded (U) conformers. At 30 bar, the native fold (N) shows disorder only in the F helix. Between 500 bar and 1200 bar, a series of locally disordered conformers I are produced, in which local disorder occurs in the C helix, the CD loop, the G helix and part of the H helix. At 2000 bar, most cross-peaks exhibit severe line-broadening, suggesting the formation of a molten globule, but at 3000 bar all the cross-peaks reappear, showing that the molten globule turns into a well-hydrated, mobile unfolded conformation U. Since all the spectral changes were reversible with pressure, apomyoglobin is considered to exist as an equilibrium mixture of the N, I, MG and U conformers at all pressures. MG is situated at 2.4+/-(0.1) kcal/mol above N at 1 bar and the unfolding transition from the combined N-I state to MG is accompanied by a loss of partial molar volume by 75+/-(3) ml/mol. On the basis of these observations, we postulate a theorem that the partial molar volume of a protein decreases in parallel with the loss of its conformational order.

subject areas

  • Apoproteins
  • Escherichia coli
  • Magnetic Resonance Spectroscopy
  • Models, Molecular
  • Myoglobin
  • Protein Conformation
  • Protein Folding
  • Thermodynamics
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Research

keywords

  • apomyoglobin
  • high pressure NMR
  • local unfolding
  • molten globule
  • volume theorem
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Identity

International Standard Serial Number (ISSN)

  • 0022-2836

Digital Object Identifier (DOI)

  • 10.1016/s0022-2836(02)00449-7

PubMed ID

  • 12079388
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Additional Document Info

start page

  • 311

end page

  • 319

volume

  • 320

issue

  • 2

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