Effects of pH, Ca2+ and lanthanides on conformation of the sarcoplasmic reticulum Ca2+-ATPase catalytic site

M. N. Ivkova, V. V. Pletnev, M. G. Vinokurov, V. A. Pechatnikov, V. G. Ivkov, I. Jona, J. Fölöp, A. Köver

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Abstract

The conformational changes at the ATP-catalytic site of the sarcoplasmic reticulum (SR) Ca2+-ATPase have been studied by the fluorescence of the fluorescein 5-isothiocyanate (FITC) bound to the adenine subsite. The FITC-SR fluorescence parameters have been examined in the pH range 5.7-8.0 in the presence of EGTA, Ca2+ or Ln3+ (La3+, Pr3+, Nd3+, Tb3+ etc.). A quantitative method to calculate the equilibrium between the protein conformers is proposed on the basis of the fluorometric titration curve analysis. The distance Nd3+-FITC was estimated to be about 1 nm at pH 6-7 and 1.7 nm at pH 8 which can be interpreted as an increase of the distance between the nucleotide and phosphorylation domains of Ca2+-ATPase in alkaline media. These studies suggest that the ligand-stabilized E1-form of Ca2+-ATPase can exist in two conformational states with the closed and opened interdomain cleft in the pH range 5.7-8.0. The pH-dependence of the ratio of these states correlates with that of the E1 ↔ E2 equilibrium without ligands. These dependences were approximated by simple Henderson-Hassellbach equations with pK 7.0 ± 0.1, i.e. the transition between two protein conformations is probably governed by one proton dissociation.

Original languageEnglish
Pages (from-to)231-238
Number of pages8
JournalBiochimica et Biophysica Acta (BBA)/Protein Structure and Molecular
Volume1118
Issue number3
DOIs
Publication statusPublished - Feb 1 1992

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Keywords

  • ATPase, Ca-
  • Catalytic site
  • Fluorescein isothiocyanate
  • Lanthanide binding
  • Sarcoplasmic reticulum

ASJC Scopus subject areas

  • Biophysics
  • Structural Biology
  • Biochemistry
  • Molecular Biology

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