Reversible folding reactions of human apolipoprotein A-I: pressure and guanidinium chloride effects

William W. Mantulin, Henry J. Pownall

Research output: Contribution to journalArticle

10 Scopus citations

Abstract

Apolipoprotein A-I, the major structural polypeptide of human high-density lipoproteins, activates lecithin: cholesterol acyltransferase, the cholesterol ester-forming enzyme in plasma. Apolipoprotein A-I, like several other apolipoproteins, exhibits structural adapatability, which is manifest in a low free energy of stabilization and facile changes in secondary structure. We have investigated the dual effects of guanidinium chloride (GdmCl) and pressure perturbation at low GdmCl concentrations on apolipoprotein A-I conformational states, using fluorescence detection. Pressure alone (up to 3 kilobar) is insufficient to fully denature apolipoprotein A-I, and results in formation of metastable state(s). However, in conjunction with low concentrations of GdmCl the calculated volume change upon pressure denaturation increases from approx. - 50 ml/mol to -90 ml/mol. The free energy of denaturation by pressure perturbation ranges from 1.4 to 1.8 kcal/mol, but the conformational states induced by pressure and GdmCl perturbation are most likely different. The physico-chemical properties of native and pressure-denatured conformational states can be, readily and reversibly, measured by fluorescence techniques. Biological activity of apolipoprotein A-I in the form of lecithin:cholesterol acyltransferase activation, is also reversible upon pressure perturbation. Samples of apolipoprotein A-I exposed to 2 kbar for an hour activated lecithin: cholesterol acyltransferase equally well as controls. To delineate more precisely the conformational states of apolipoprotein A-I under pressure, time-dependent anisotropy decay measurements, capable of resolving rotational heterogeneity, will be required.

Original languageEnglish (US)
Pages (from-to)215-221
Number of pages7
JournalBiochimica et Biophysica Acta (BBA)/Lipids and Lipid Metabolism
Volume836
Issue number2
DOIs
StatePublished - Sep 11 1985

Keywords

  • (Human HDL)
  • Apolipoprotein A-I
  • cholesterol acyltransferase
  • Guanidinium chloride
  • Hydrostatic pressure
  • Lecithin
  • Protein denaturation

ASJC Scopus subject areas

  • Endocrinology
  • Biophysics
  • Biochemistry

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