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pH-dependent conformational changes of wheat germ calmodulin.

C L Wang1

  • 1Department of Muscle Research, Boston Biomedical Research Institute, Massachusetts 02114.

Biochemistry
|May 30, 1989
PubMed
Summary

Wheat germ calmodulin undergoes conformational changes. At neutral pH, it is compact, but at pH 5, it elongates, as shown by fluorescence energy transfer measurements.

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Area of Science:

  • Biochemistry
  • Molecular Biology
  • Biophysics

Background:

  • Calmodulin is a crucial calcium-binding protein involved in cellular signaling.
  • Understanding calmodulin's conformational dynamics is key to elucidating its function.
  • Wheat germ calmodulin serves as a model system for studying calmodulin structure-function relationships.

Purpose of the Study:

  • To investigate the conformational changes of wheat germ calmodulin in response to pH variations.
  • To measure the interdomain distance within wheat germ calmodulin using fluorescence energy transfer (FRET).

Main Methods:

  • Fluorescence energy transfer (FRET) measurements utilizing terbium ions (Tb3+) as donors and a specific organic chromophore as an acceptor.
  • Labeling of wheat germ calmodulin at cysteine residue 27 with the acceptor chromophore.
  • pH-dependent luminescence lifetime measurements of Tb3+ bound to Ca2+-binding sites.
  • Limited proteolysis with trypsin in the presence of Ca2+ to generate protein fragments.

Main Results:

  • At neutral pH, FRET efficiency indicated a compact conformation of wheat germ calmodulin.
  • At pH 5, a decrease in FRET efficiency (unquenching of Tb3+ emission) suggested an elongated conformation.
  • Limited proteolysis abolished the pH-dependent changes in Tb3+ emission decay, indicating domain-specific conformational alterations.

Conclusions:

  • Wheat germ calmodulin exhibits pH-dependent conformational flexibility, transitioning from a compact state near neutral pH to a more elongated state at pH 5.
  • These findings are analogous to conformational changes observed in rabbit skeletal troponin C.
  • The study provides insights into the structural basis of calmodulin's function and calcium-dependent regulation.

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