title: A unique EF-hand motif in mnemiopsin photoprotein from Mnemiopsis leidyi: implication for its low calcium sensitivity.
abstract: Up to now, all reported Ca(2+)-regulated photoproteins, except for mnemiopsin, have been cloned and expressed in Escherichia coli. In this study, the cDNA for an isotype of mnemiopsin, from the ctenophore Mnemiopsis leidyi, has been cloned, sequenced, and functionally expressed. The full length cDNA encoding mnemiopsin of M. leidyi was 624 bp open reading frame encoding a protein of 207 amino acid residues with calculated molecular mass of ∼24 kDa. The deduced amino acid sequence showed 90% and 84% identity to berovine (from ctenophore Beroe abyssicola) and bolinopsin 2 (from the ctenophore Bolinopsis infundibulum) respectively. In contrast to all known EF-hand in photoproteins, a unique EF-hand motif was found in mnemiopsin, in which a conserved glycine is substituted with glutamic acid. According to the results, the optimum pH was 9.0, time course of regeneration was 15 h and its Ca(2+) sensitivity was lower than aequorin. Results of pK(a) calculation for ionizable residues, motif scan and hydrophobic interactions of cavity aromatic residues of mnemiopsin in comparison with aequorin showed different patterns in these two photoproteins. In addition, experimental results are confirmed with the theoretical studies.
authors.affiliation: Department of Biology, Faculty of Sciences, University of Guilan, Rasht, Iran.
authors.forename: Vahab
authors.initials: V
authors.lastname: Jafarian
authors.forename: Reyhaneh
authors.initials: R
authors.lastname: Sariri
authors.forename: Saman
authors.initials: S
authors.lastname: Hosseinkhani
authors.forename: Mahmoud-Reza
authors.initials: MR
authors.lastname: Aghamaali
authors.forename: Reza Hassan
authors.initials: RH
authors.lastname: Sajedi
authors.forename: Majid
authors.initials: M
authors.lastname: Taghdir
authors.forename: Sadegh
authors.initials: S
authors.lastname: Hassannia
mesh_terms: D000331:Aequorin / Q000737:chemistry; D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D037302:Ctenophora / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007093:Imidazoles / Q000737:chemistry; D008164:Luminescent Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D011487:Protein Conformation; D011719:Pyrazines / Q000737:chemistry
chemical_list: D007093:Imidazoles; D008164:Luminescent Proteins; D011719:Pyrazines; C010245:mnemiopsin; C010497:obelin; C017144:coelenterazine; D000331:Aequorin; D002118:Calcium