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Related Experiment Videos

pH-induced changes in G-actin conformation and metal affinity.

C T Zimmerle1, C Frieden

  • 1Department of Biological Chemistry, Washington University School of Medicine, St. Louis, Missouri 63110.

Biochemistry
|October 4, 1988
PubMed
Summary

Investigating actin’s response to metal ions at different pH levels reveals protonation effects. Changes in fluorescence indicate pH alters actin’s conformation, influencing cation binding and protein structure.

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Area of Science:

  • Biochemistry
  • Biophysics
  • Protein Dynamics

Background:

  • Actin conformational changes are crucial for cellular functions.
  • Metal ions like Ca2+ and Mg2+ influence actin structure and dynamics.
  • Understanding pH-dependent effects provides insights into protein regulation.

Purpose of the Study:

  • To investigate metal-induced conformational changes in G-actin as a function of pH.
  • To elucidate the role of protonation in modulating cation binding and actin structure.
  • To characterize the pH-dependent fluorescence changes of labeled actin.

Main Methods:

  • G-actin was labeled at Cys-374 with a fluorescent probe.
  • Fluorescence spectroscopy was used to monitor conformational changes.

Related Experiment Videos

  • Experiments were conducted across a range of pH values and divalent cation concentrations (Ca2+, Mg2+).

    • Main Results:

    • High Ca2+ and Mg2+ concentrations induced distinct instantaneous and slow fluorescence increases at pH 8.
    • Lowering pH reduced the magnitude of Mg2+-induced fluorescence changes.
    • Ca2+ (low/moderate concentrations) induced a pH-dependent fluorescence increase, suggesting protonation effects.
    • A single class of residues with pK ~6.8 appears involved in pH-dependent conformational changes.

    Conclusions:

    • Protonation of specific actin residues (pK ~6.8) alters the protein's conformation.
    • This protonation affects the fluorescence response to cation binding at moderate-affinity sites.
    • Actin conformation changes induced by protonation resemble those from low-affinity cation binding.