title: Biohybrid photosynthetic antenna complexes for enhanced light-harvesting.
abstract: Biohybrid antenna systems have been constructed that contain synthetic chromophores attached to 31mer analogues of the bacterial photosynthetic core light-harvesting (LH1) β-polypeptide. The peptides are engineered with a Cys site for bioconjugation with maleimide-terminated chromophores, which include synthetic bacteriochlorins (BC1, BC2) with strong near-infrared absorption and commercial dyes Oregon green (OGR) and rhodamine red (RR) with strong absorption in the blue-green to yellow-orange regions. The peptides place the Cys 14 (or 6) residues before a native His site that binds bacteriochlorophyll a (BChl-a) and, like the native LH proteins, have high helical content as probed by single-reflection IR spectroscopy. The His residue associates with BChl-a as in the native LH1 β-polypeptide to form dimeric ββ-subunit complexes [31mer(-14Cys)X/BChl](2), where X is one of the synthetic chromophores. The native-like BChl-a dimer has Q(y) absorption at 820 nm and serves as the acceptor for energy from light absorbed by the appended synthetic chromophore. The energy-transfer characteristics of biohybrid complexes have been characterized by steady-state and time-resolved fluorescence and absorption measurements. The quantum yields of energy transfer from a synthetic chromophore located 14 residues from the BChl-coordinating His site are as follows: OGR (0.30) < RR (0.60) < BC2 (0.90). Oligomeric assemblies of the subunit complexes [31mer(-14Cys)X/BChl](n) are accompanied by a bathochromic shift of the Q(y) absorption of the BChl-a oligomer as far as the 850-nm position found in cyclic native photosynthetic LH2 complexes. Room-temperature stabilized oligomeric biohybrids have energy-transfer quantum yields comparable to those of the dimeric subunit complexes as follows: OGR (0.20) < RR (0.80) < BC1 (0.90). Thus, the new biohybrid antennas retain the energy-transfer and self-assembly characteristics of the native antenna complexes, offer enhanced coverage of the solar spectrum, and illustrate a versatile paradigm for the construction of artificial LH systems.
authors.affiliation: Department of Chemistry, Washington University, St. Louis, Missouri 63130-4889, United States.
authors.forename: Joseph W
authors.initials: JW
authors.lastname: Springer
authors.forename: Pamela S
authors.initials: PS
authors.lastname: Parkes-Loach
authors.forename: Kanumuri Ramesh
authors.initials: KR
authors.lastname: Reddy
authors.forename: Michael
authors.initials: M
authors.lastname: Krayer
authors.forename: Jieying
authors.initials: J
authors.lastname: Jiao
authors.forename: Gregory M
authors.initials: GM
authors.lastname: Lee
authors.forename: Dariusz M
authors.initials: DM
authors.lastname: Niedzwiedzki
authors.forename: Michelle A
authors.initials: MA
authors.lastname: Harris
authors.forename: Christine
authors.initials: C
authors.lastname: Kirmaier
authors.forename: David F
authors.initials: DF
authors.lastname: Bocian
authors.forename: Jonathan S
authors.initials: JS
authors.lastname: Lindsey
authors.forename: Dewey
authors.initials: D
authors.lastname: Holten
authors.forename: Paul A
authors.initials: PA
authors.lastname: Loach
mesh_terms: D000595:Amino Acid Sequence; D008027:Light; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010788:Photosynthesis; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D045342:Light-Harvesting Protein Complexes