title: Photocurrent and electronic activities of oriented-His-tagged photosynthetic light-harvesting/reaction center core complexes assembled onto a gold electrode.
abstract: A polyhistidine (His) tag was fused to the C- or N-terminus of the light-harvesting (LH1)-α chain of the photosynthetic antenna core complex (LH1-RC) from  Rhodobacter sphaeroides  to allow immobilization of the complex on a solid substrate with defined orientation. His-tagged LH1-RCs were adsorbed onto a gold electrode modified with Ni-NTA. The LH1-RC with the C-terminal His-tag (C-His LH1-RC) on the modified electrode produced a photovoltaic response upon illumination. Electron transfer is unidirectional within the RC and starts when the bacteriochlorophyll a dimer in the RC is activated by light absorbed by LH1. The LH1-RC with the N-terminal His-tag (N-His LH1-RC) produced very little or no photocurrent upon illumination at any wavelength. The conductivity of the His-tagged LH1-RC was measured with point-contact current imaging atomic force microscopy, indicating that 60% of the C-His LH1-RC are correctly oriented (N-His 63%). The oriented C-His LH1-RC or N-His LH1-RC showed semiconductive behavior, that is, had the opposite orientation. These results indicate that the His-tag successfully controlled the orientation of the RC on the solid substrate, and that the RC produced photocurrent depending upon the orientation on the electrode.
authors.affiliation: Department of Frontier Materials, Tsukuri College, Graduate School of Engineering,  Nagoya Institute of Technology , Gokiso-cho, Showa-ku, Nagoya 466-8555, Japan.
authors.forename: Masaharu
authors.initials: M
authors.lastname: Kondo
authors.forename: Kouji
authors.initials: K
authors.lastname: Iida
authors.forename: Takehisa
authors.initials: T
authors.lastname: Dewa
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Tanaka
authors.forename: Takuji
authors.initials: T
authors.lastname: Ogawa
authors.forename: Sakiko
authors.initials: S
authors.lastname: Nagashima
authors.forename: Kenji V P
authors.initials: KV
authors.lastname: Nagashima
authors.forename: Keizo
authors.initials: K
authors.lastname: Shimada
authors.forename: Hideki
authors.initials: H
authors.lastname: Hashimoto
authors.forename: Alastair T
authors.initials: AT
authors.lastname: Gardiner
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Cogdell
authors.forename: Mamoru
authors.initials: M
authors.lastname: Nango
mesh_terms: D000327:Adsorption; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D025541:Bacteriochlorophyll A / Q000737:chemistry / Q000378:metabolism; D040761:Biomimetic Materials / Q000737:chemistry* / Q000378:metabolism; D004553:Electric Conductivity; D004566:Electrodes; D004579:Electron Transport; D004581:Electronics; D006046:Gold; D006639:Histidine / Q000737:chemistry; D008027:Light; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D018625:Microscopy, Atomic Force; D010788:Photosynthesis; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012242:Rhodobacter sphaeroides / Q000737:chemistry*; D012993:Solar Energy
chemical_list: D001426:Bacterial Proteins; D025541:Bacteriochlorophyll A; D045342:Light-Harvesting Protein Complexes; D011994:Recombinant Proteins; C033223:polyhistidine; D006639:Histidine; D006046:Gold