title: A circumventing role for the non-native intermediate in the folding of β-lactoglobulin.
abstract: Folding experiments have suggested that some proteins have kinetic intermediates with a non-native structure. A simple G ̅o model does not explain such non-native intermediates. Therefore, the folding energy landscape of proteins with non-native intermediates should have characteristic properties. To identify such properties, we investigated the folding of bovine β-lactoglobulin (βLG). This protein has an intermediate with a non-native α-helical structure, although its native form is predominantly composed of β-structure. In this study, we prepared mutants whose α-helical and β-sheet propensities are modified and observed their folding using a stopped-flow circular dichroism apparatus. One interesting finding was that E44L, whose β-sheet propensity was increased, showed a folding intermediate with an amount of β-structure similar to that of the wild type, though its folding took longer. Thus, the intermediate seems to be a trapped intermediate. The high α-helical propensity of the wild-type sequence likely causes the folding pathway to circumvent such time-consuming intermediates. We propose that the role of the non-native intermediate is to control the pathway at the beginning of the folding reaction.
authors.affiliation: Institute for Protein Research, Osaka University, 3-2 Yamadaoka, Suita, Osaka 565-0871, Japan.
authors.forename: Kazumasa
authors.initials: K
authors.lastname: Sakurai
authors.forename: Shunsuke
authors.initials: S
authors.lastname: Fujioka
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Konuma
authors.forename: Masanori
authors.initials: M
authors.lastname: Yagi
authors.forename: Yuji
authors.initials: Y
authors.lastname: Goto
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002417:Cattle; D002942:Circular Dichroism; D019791:Guanidine / Q000494:pharmacology; D007700:Kinetics; D007782:Lactoglobulins / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D017510:Protein Folding / Q000187:drug effects; D058849:Protein Refolding / Q000187:drug effects; D055550:Protein Stability / Q000187:drug effects; D017433:Protein Structure, Secondary
chemical_list: D007782:Lactoglobulins; D050505:Mutant Proteins; D019791:Guanidine