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Ca2+ Binding and Conformational Switch of the Photoprotein Mnemiopsin
Shima Tarahomi1, Reza H Sajedi2, Hossein Rahmani2
1Department of Biology, Faculty of Sciences, University of Guilan, Rasht, Iran.
Protein and Peptide Letters
|March 16, 2017
Summary
Calcium binding causes apo-mnemiopsin to become more flexible, which is crucial for its bioluminescence. This study reveals Ca2+-depleted photoproteins adopt a closed conformation, while Ca2+-loaded forms are more open and flexible.
Area of Science:
- Biochemistry
- Structural Biology
- Biophysics
Background:
- Bioluminescence relies on Ca2+-binding photoproteins undergoing intramolecular reactions triggered by calcium ions.
- Apo-mnemiopsin, a Ca2+-binding photoprotein, was studied in Ca2+-depleted and Ca2+-loaded states to understand structural changes upon calcium binding.
Purpose of the Study:
- To investigate the structural transition of apo-mnemiopsin induced by calcium (Ca2+) binding.
- To compare the structural and dynamic properties of Ca2+-depleted and Ca2+-loaded apo-mnemiopsin.
Main Methods:
- UV-visible, Circular Dichroism (CD), and fluorescence spectroscopy were employed.
- Dynamic quenching and limited proteolysis analyses were performed.
- Trichloroacetic acid (TCA) precipitation was used to obtain Ca2+-depleted apo-mnemiopsin.
Main Results:
- Ca2+ binding causes apo-mnemiopsin's overall structure to open in a concentration-dependent manner, without significantly altering secondary structure.
- Ca2+-depleted apo-mnemiopsin adopts a closed conformation, unlike the more open Ca2+-loaded form.
- Ca2+-loaded apo-mnemiopsin exhibits increased flexibility compared to its Ca2+-free state.
Conclusions:
- Increased protein flexibility upon calcium binding is critical for the oxidative decarboxylation of coelenterazine.
- This flexibility facilitates the bioluminescence reaction, leading to light emission.
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