title: Time-resolved small-angle X-ray scattering investigation of the folding dynamics of heme oxygenase: implication of the scaling relationship for the submillisecond intermediates of protein folding.
abstract: Polypeptide collapse is generally observed as the initial folding dynamics of proteins with more than 100 residues, and is suggested to be caused by the coil-globule transition explained by Flory's theory of polymers. To support the suggestion by establishing a scaling behavior between radius of gyration (Rg) and chain length for the initial folding intermediates, the folding dynamics of heme oxygenase (HO) was characterized by time-resolved, small-angle X-ray scattering. HO is a highly helical protein without disulfide bridges, and is the largest protein (263 residues) characterized by the method. The folding process of HO was found to contain a transient oligomerization; however, the conformation within 10 ms was demonstrated to be monomeric and to possess Rg of 26.1(+/-1.1) A. Together with the corresponding data for proteins with different chain lengths, the seven Rg values demonstrated the scaling relationship to chain length with a scaling exponent of 0.35+/-0.11, which is close to the theoretical value of 1/3 predicted for globules in solutions where monomer-monomer interactions are favored over monomer-solvent interactions (poor solvent). The finding indicated that the initial folding dynamics of proteins bears the signature of the coil-globule transition, and offers a clue to explain the folding mechanisms of proteins with different chain lengths.
authors.affiliation: Graduate School of Engineering, Kyoto University, Kyoto 615-8510, Japan.
authors.forename: Takanori
authors.initials: T
authors.lastname: Uzawa
authors.forename: Tetsunari
authors.initials: T
authors.lastname: Kimura
authors.forename: Koichiro
authors.initials: K
authors.lastname: Ishimori
authors.forename: Isao
authors.initials: I
authors.lastname: Morishima
authors.forename: Toshitaka
authors.initials: T
authors.lastname: Matsui
authors.forename: Masao
authors.initials: M
authors.lastname: Ikeda-Saito
authors.forename: Satoshi
authors.initials: S
authors.lastname: Takahashi
authors.forename: Shuji
authors.initials: S
authors.lastname: Akiyama
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Fujisawa
mesh_terms: D000818:Animals; D002942:Circular Dichroism; D006419:Heme Oxygenase (Decyclizing) / Q000737:chemistry* / Q000378:metabolism*; D007527:Isoenzymes / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D011489:Protein Denaturation; D017510:Protein Folding; D051381:Rats; D012542:Scattering, Radiation; D013050:Spectrometry, Fluorescence; D014965:X-Rays
chemical_list: D007527:Isoenzymes; D006419:Heme Oxygenase (Decyclizing)