title: Interaction Site between the Protein Aggregates and Thiocyanate Ion in Aqueous Solution: A Case Study of 1-Butyl-3-methylimidazolium Thiocyanate.
abstract: To investigate the interaction site between amyloid-like protein aggregates and thiocyanate (SCN(-)) ion, we studied the relationship between protein aggregation (cytochrome c, myoglobin, lysozyme, ribonuclease A, and β-lactoglobulin) and SCN(-) ion in aqueous 1-butyl-3-methylimidazolium thiocyanate ([bmim][SCN]) solutions using optical spectroscopy. The addition of [bmim][SCN] (>10 mol % IL) to a protein solution induced protein aggregation owing to the intermolecular β-sheet structures except in the case of cytochrome c. Analysis of the content of 20 amino acid residues for each protein revealed that the degree of intermolecular β-sheet structures (β%) and midpoint concentration from the unfolding to aggregation state ([IL]1/2(U →βA)) is correlated primarily with the content of Lys residue in proteins (correlation coefficient (R(2)) = 0.97). The attractive interaction between the SCN(-) ions and NH3(+) groups of the side chain terminal of Lys residue inhibits protein aggregation owing to the intermolecular β-sheet structure. This finding might be related to the mechanism for the solubilization of amyloid aggregates by strong denaturants containing SCN(-) ions such as guanidine thiocyanate.
authors.affiliation: †Department of Applied Chemistry, National Defense Academy, 1-10-20 Hashirimizu, Yokosuka, Kanagawa 239-8686, Japan.
authors.forename: Takahiro
authors.initials: T
authors.lastname: Takekiyo
authors.affiliation: †Department of Applied Chemistry, National Defense Academy, 1-10-20 Hashirimizu, Yokosuka, Kanagawa 239-8686, Japan.
authors.forename: Erika
authors.initials: E
authors.lastname: Yamaguchi
authors.affiliation: ‡Department of Chemistry, Faculty of Science, Fukuoka University, Nanakuma, Jonan-ku, Fukuoka, Fukuoka 814-0810, Japan.
authors.forename: Koji
authors.initials: K
authors.lastname: Yoshida
authors.affiliation: §Department of Pharmacy, Ritsumeikan University, 1-1-1 Noji-Higashi, Kusatsu, Shiga 525-8577, Japan.
authors.forename: Minoru
authors.initials: M
authors.lastname: Kato
authors.affiliation: ‡Department of Chemistry, Faculty of Science, Fukuoka University, Nanakuma, Jonan-ku, Fukuoka, Fukuoka 814-0810, Japan.
authors.forename: Toshio
authors.initials: T
authors.lastname: Yamaguchi
authors.affiliation: †Department of Applied Chemistry, National Defense Academy, 1-10-20 Hashirimizu, Yokosuka, Kanagawa 239-8686, Japan.
authors.forename: Yukihiro
authors.initials: Y
authors.lastname: Yoshimura
mesh_terms: D000818:Animals; D001665:Binding Sites; D002415:Cats; D007093:Imidazoles / Q000737:chemistry*; D008958:Models, Molecular; D066329:Protein Aggregates; D017433:Protein Structure, Secondary; D011506:Proteins / Q000737:chemistry*; D012996:Solutions; D013861:Thiocyanates / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: C525963:1-butyl-3-methylimidazolium; D007093:Imidazoles; D066329:Protein Aggregates; D011506:Proteins; D012996:Solutions; D013861:Thiocyanates; D014867:Water; C031760:thiocyanate