1. Ca2+ Binding and Conformational Switch of the Photoprotein Mnemiopsin
- Author
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Tarahomi, Shima, Sajedi, Reza H., Rahmani, Hossein, Ranjbar, Bijan, and Taghdir, Majid
- Abstract
Background: Bioluminescence in Ca2+-binding photoproteins is an intramolecular reaction triggered by the addition of Ca2+. A comparative study has been done on Ca2+-depleted and Ca2+-loaded apo-mnemiopsin to understand the structural transition of the photoprotein by Ca2+ binding. Ca2+ is removed by TCA (trichloroacetic acid) precipitation to obtain Ca2+-depleted apomnemiopsin. Method: UV–visible, CD and fluorescence spectroscopic studies demonstrate that the addition of Ca2+ is brought about by the overall structure of apo-mnemiopsin becomes more open in a concentration- dependent manner without significantly influencing the secondary structure and indicate that the Ca2+-depleted form of apo-mnemiopsin, in contrast to most other EF-hand calcium binding proteins, adopt a closed conformation when compared to the Ca2+-loaded form. On the other hand, dynamic quenching and limited proteolysis analysis revealed that Ca2+-loaded apo-mnemiopsin became much more flexible than Ca2+ free apo-mnemiopsin. Results: It seems that increased flexibility of the protein, which occurs due to calcium binding, is a critical factor in oxidative decarboxylation reaction on coelenterazine and consequently light emission.
- Published
- 2017
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