title: Cytochrome c polymerization by successive domain swapping at the C-terminal helix.
abstract: Cytochrome c (cyt c) is a stable protein that functions in a monomeric state as an electron donor for cytochrome c oxidase. It is also released to the cytosol when permeabilization of the mitochondrial outer membrane occurs at the early stage of apoptosis. For nearly half a century, it has been known that cyt c forms polymers, but the polymerization mechanism remains unknown. We found that cyt c forms polymers by successive domain swapping, where the C-terminal helix is displaced from its original position in the monomer and Met-heme coordination is perturbed significantly. In the crystal structures of dimeric and trimeric cyt c, the C-terminal helices are replaced by the corresponding domain of other cyt c molecules and Met80 is dissociated from the heme. The solution structures of dimeric, trimeric, and tetrameric cyt c were linear based on small-angle X-ray scattering measurements, where the trimeric linear structure shifted toward the cyclic structure by addition of PEG and (NH(4))(2)HPO(4). The absorption and CD spectra of high-order oligomers (approximately 40 mer) were similar to those of dimeric and trimeric cyt c but different from those of monomeric cyt c. For dimeric, trimeric, and tetrameric cyt c, the DeltaH of the oligomer dissociation to monomers was estimated to be about -20 kcal/mol per protomer unit, where Met-heme coordination appears to contribute largely to DeltaH. The present results suggest that cyt c polymerization occurs by successive domain swapping, which may be a common mechanism of protein polymerization.
authors.affiliation: Graduate School of Materials Science, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0192, Japan. hirota@ms.naist.jp
authors.forename: Shun
authors.initials: S
authors.lastname: Hirota
authors.forename: Yoko
authors.initials: Y
authors.lastname: Hattori
authors.forename: Satoshi
authors.initials: S
authors.lastname: Nagao
authors.forename: Midori
authors.initials: M
authors.lastname: Taketa
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Komori
authors.forename: Hironari
authors.initials: H
authors.lastname: Kamikubo
authors.forename: Zhonghua
authors.initials: Z
authors.lastname: Wang
authors.forename: Isao
authors.initials: I
authors.lastname: Takahashi
authors.forename: Shigeru
authors.initials: S
authors.lastname: Negi
authors.forename: Yukio
authors.initials: Y
authors.lastname: Sugiura
authors.forename: Mikio
authors.initials: M
authors.lastname: Kataoka
authors.forename: Yoshiki
authors.initials: Y
authors.lastname: Higuchi
mesh_terms: D000818:Animals; D001704:Biopolymers / Q000378:metabolism*; D002152:Calorimetry, Differential Scanning; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D045304:Cytochromes c / Q000737:chemistry* / Q000378:metabolism*; D006736:Horses; D010084:Oxidation-Reduction; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D053838:Scattering, Small Angle; D012996:Solutions; D013329:Structure-Activity Relationship
chemical_list: D001704:Biopolymers; D012996:Solutions; D045304:Cytochromes c