title: Determination of structural elements on the folding reaction of mnemiopsin by spectroscopic techniques.
abstract: Mnemiopsin 1 is a member of photoprotein family, made up of 206 amino acid residues. These Ca(2+)-regulated photoproteins are responsible for light emission in a variety of marine cnidarians and ctenophores. They composed of an apoprotein, a single polypeptide chain of 25 kDa, molecular oxygen and the non-covalently bound chromophore. In this study, we examined whether three mutations, namely R39K, S128G and V183T affect the thermodynamic stability as well as refolding and unfolding kinetics of mnemiopsin 1. Conformational stability measurements using fluorescence and far-UV CD spectroscopies revealed that all variants unfold in multi-step manner in which the secondary and tertiary structures are lost in different steps. However kinetic studies showed that point mutation S128G destabilizes both kinetic intermediate and native conformation; while, these structural elements are stabilized in V183T. We also found that the stability of folded and intermediate states increases in R39K. We concluded that the initial packing of helical segments within the protein structure is more facilitated when Lys with smaller side chain is present in the protein chain.
authors.affiliation: Department of Biophysics, Faculty of Biological Sciences, Tarbiat Modares University, P.O. Box 14115-175, Tehran, Iran.
authors.forename: Forough
authors.initials: F
authors.lastname: Hakiminia
authors.affiliation: Department of Biology, Faculty of Sciences, University of Zanjan, P.O. Box 45195-313, Zanjan, Iran.
authors.forename: Khosrow
authors.initials: K
authors.lastname: Khalifeh
authors.affiliation: Department of Biochemistry, Faculty of Biological Sciences, Tarbiat Modares University, P.O. Box 14115-175, Tehran, Iran.
authors.forename: Reza H
authors.initials: RH
authors.lastname: Sajedi
authors.affiliation: Department of Biophysics, Faculty of Biological Sciences, Tarbiat Modares University, P.O. Box 14115-175, Tehran, Iran. Electronic address: ranjbarb@modares.ac.ir.
authors.forename: Bijan
authors.initials: B
authors.lastname: Ranjbar
mesh_terms: D000818:Animals; D002942:Circular Dichroism; D007700:Kinetics; D008164:Luminescent Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D011489:Protein Denaturation / Q000187:drug effects; D017510:Protein Folding / Q000187:drug effects; D017433:Protein Structure, Secondary; D013050:Spectrometry, Fluorescence; D013816:Thermodynamics; D014508:Urea / Q000494:pharmacology
chemical_list: D008164:Luminescent Proteins; D050505:Mutant Proteins; C010245:mnemiopsin; D014508:Urea
keywords: Intermediate; Kinetics; Photoprotein; Refolding; Thermodynamic stability; Unfolding