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Apo-parvalbumin as an intrinsically disordered protein
Sergei E Permyakov1, Anush G Bakunts, Alexander I Denesyuk
1Institute for Biological Instrumentation of the Russian Academy of Sciences, Pushchino, Moscow Region 142290, Russia.
Proteins
|February 9, 2008
Summary
Pike parvalbumin (PA) in its calcium-free (apo) state is an intrinsically disordered protein (IDP). Calcium binding induces a rigid structure, essential for muscle relaxation regulation.
Area of Science:
- Biochemistry
- Structural Biology
- Protein Science
Background:
- Intrinsically disordered proteins (IDPs) lack stable tertiary structures but perform vital functions.
- Parvalbumin (PA) is a calcium-binding protein crucial for fast muscle relaxation.
Purpose of the Study:
- To investigate whether the calcium-free (apo) state of pike parvalbumin (PA) exhibits intrinsically disordered protein characteristics.
- To elucidate the structural changes upon calcium binding and its role in PA's function.
Main Methods:
- Differential scanning calorimetry (DSC) to assess thermal stability.
- Circular dichroism (CD) spectroscopy (far-UV and near-UV) to monitor structural changes.
- Fluorescence spectroscopy using bis-ANS to probe hydrophobic exposure.
- Guanidinium chloride-induced unfolding experiments.
- Theoretical energetic estimations.
Main Results:
- Apo-PA lacks thermally induced transitions with measurable enthalpy, indicating a lack of rigid tertiary structure.
- Calcium removal increases hydrophobicity and reduces alpha-helical content, suggesting disorder.
- CD spectroscopy revealed a lack of fixed tertiary structure and complex denaturation behavior, including cold denaturation.
- Calorimetric and titration data confirmed that calcium binding induces the native, rigid structure.
Conclusions:
- Pike parvalbumin in its apo-state is an intrinsically disordered protein.
- Calcium ions are essential for stabilizing the rigid tertiary structure of PA, enabling its function in muscle relaxation.
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