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Intermediate conformational states of apocytochrome c
Biochemistry
|October 5, 1993
Summary
Horse apocytochrome c protein structure is not always unfolded. High salt concentrations and specific anions like perchlorate stabilize secondary structures, revealing distinct conformational states dependent on pH and ionic strength.
Area of Science:
- Biochemistry
- Protein Chemistry
- Structural Biology
Background:
- Horse apocytochrome c is generally considered an unfolded protein.
- Understanding protein conformational changes is crucial in biochemistry.
Purpose of the Study:
- To investigate the conformational states of horse apocytochrome c under varying pH and salt conditions.
- To characterize the influence of anions, specifically perchlorate, on protein structure.
Main Methods:
- Circular dichroism spectroscopy (far- and near-UV) to assess secondary structure.
- Fluorescence labeling of cysteine residues with IAEDANS for conformational analysis.
- Fluorescence energy transfer (FRET) measurements to determine protein compactness.
Main Results:
- At low ionic strength, protein structure is unfolded across a wide pH range.
- High salt concentrations, particularly perchlorate, induce significant secondary structure at acidic and neutral pH.
- Perchlorate stabilizes an intermediate 'A state' with molten globule-like characteristics at low pH.
- FRET analysis reveals pH-dependent compaction at low ionic strength and salt-dependent compaction at acidic pH with perchlorate.
Conclusions:
- Horse apocytochrome c exhibits complex conformational behavior influenced by pH, ionic strength, and specific anions.
- The protein can adopt structured states, challenging the assumption of it being solely unfolded.
- Perchlorate plays a key role in stabilizing intermediate conformational states.