title: Specific collapse followed by slow hydrogen-bond formation of beta-sheet in the folding of single-chain monellin.
abstract: Characterization of the conformational landscapes for proteins with different secondary structures is important in elucidating the mechanism of protein folding. The folding trajectory of single-chain monellin composed of a five-stranded beta-sheet and a helix was investigated by using a pH-jump from the alkaline unfolded to native state. The kinetic changes in the secondary structures and in the overall size and shape were measured by circular dichroism spectroscopy and small-angle x-ray scattering, respectively. The formation of the tertiary structure was monitored by intrinsic and extrinsic fluorescence. A significant collapse was observed within 300 micros after the pH-jump, leading to the intermediate with a small amount of secondary and tertiary structures but with an overall oblate shape. Subsequently, the stepwise formation of secondary and tertiary structures was detected. The current observation was consistent with the theoretical prediction that a more significant collapse precedes the formation of secondary structures in the folding of beta-sheet proteins than that of helical proteins [Shea, J. E., Onuchic, J. N. & Brooks, C. L., III (2002) Proc. Natl. Acad. Sci. USA 99, 16064-16068]. Furthermore, it was implied that the initial collapse was promoted by the formation of some specific structural elements, such as tight turns, to form the oblate shape.
authors.affiliation: Department of Molecular Engineering, Graduate School of Engineering, Kyoto University, Nishikyo, Kyoto 615-8510, Japan.
authors.forename: Tetsunari
authors.initials: T
authors.lastname: Kimura
authors.forename: Takanori
authors.initials: T
authors.lastname: Uzawa
authors.forename: Koichiro
authors.initials: K
authors.lastname: Ishimori
authors.forename: Isao
authors.initials: I
authors.lastname: Morishima
authors.forename: Satoshi
authors.initials: S
authors.lastname: Takahashi
authors.forename: Takashi
authors.initials: T
authors.lastname: Konno
authors.forename: Shuji
authors.initials: S
authors.lastname: Akiyama
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Fujisawa
mesh_terms: D002942:Circular Dichroism; D005453:Fluorescence; D006860:Hydrogen Bonding; D010940:Plant Proteins / Q000737:chemistry*; D011487:Protein Conformation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D012542:Scattering, Radiation; D014965:X-Rays
chemical_list: D010940:Plant Proteins; C002541:monellin protein, Dioscoreophyllum cumminsii