Ionic liquid-induced formation of the α-helical structure of β-lactoglobulin.
Structural modification of bovine milk β-lactoglobulin (β-LG) in aqueous 1-butyl-3-methylimidazolium nitrate ([bmim][NO3]) and ethylammonium nitrate ([EAN][NO3]) solutions has been investigated by Fourier transform infrared and circular dichroism spectroscopy. Remarkably, high ionic liquid (IL) concentrations (>15 mol %IL) caused formation of a non-native α-helical structure of β-LG and disruption of its tertiary structure. Furthermore, while [bmim][NO3] promoted protein aggregation, [EAN][NO3] inhibited it probably owing to differences in the unique solution structure (nanoheterogeneity) of the ILs by the different cationic species. The IL-induced α-helical formation of β-LG shows a behavior similar to the alcohol denaturation, but a disordered structure-rich state was observed in the β-α transition process by adding IL, in contrast to the case of an aqueous alcohol solution of protein. We propose that the molten salt-like property of aqueous IL solutions strongly support α-helical formation of proteins.
Department of Applied Chemistry, National Defense Academy, 1-10-20, Hashirimizu, Yokosuka, Japan 239-8686. take214@nda.ac.jp
Takahiro
T
Takekiyo
Yoshihiro
Y
Koyama
Kumiko
K
Yamazaki
Hiroshi
H
Abe
Yukihiro
Y
Yoshimura
D000818:Animals; D002417:Cattle; D002942:Circular Dichroism; D007093:Imidazoles / Q000737:chemistry; D052578:Ionic Liquids / Q000737:chemistry*; D007782:Lactoglobulins / Q000737:chemistry* / Q000378:metabolism; D011489:Protein Denaturation; D017433:Protein Structure, Secondary; D017550:Spectroscopy, Fourier Transform Infrared; D014867:Water / Q000737:chemistry
C522540:1-butyl-3-methylimidazolium nitrate; D007093:Imidazoles; D052578:Ionic Liquids; D007782:Lactoglobulins; D014867:Water