Shima Tarahomi, Reza H. Sajedi*, Hossein Rahmani, Bijan Ranjbar and Majid Taghdir Pages 476 - 482 ( 7 )
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.
EF-hand calcium-binding proteins, photoproteins, mnemiopsin, conformational switch, flexibility, proteolysis.
Department of Biology, Faculty of Sciences, University of Guilan, Rasht, Department of Biochemistry, Faculty of Biological Sciences, Tarbiat modares University, Tehran, Department of Biochemistry, Faculty of Biological Sciences, Tarbiat modares University, Tehran, Department of Biophysics, Faculty of Biological Sciences, Tarbiat modares University, Tehran, Department of Biophysics, Faculty of Biological Sciences, Tarbiat modares University, Tehran