title: Photo-oxidation of tyrosine in a bio-engineered bacterioferritin 'reaction centre'-a protein model for artificial photosynthesis.
abstract: The photosynthetic reaction centre (RC) is central to the conversion of solar energy into chemical energy and is a model for bio-mimetic engineering approaches to this end. We describe bio-engineering of a Photosystem II (PSII) RC inspired peptide model, building on our earlier studies. A non-photosynthetic haem containing bacterioferritin (BFR) from Escherichia coli that expresses as a homodimer was used as a protein scaffold, incorporating redox-active cofactors mimicking those of PSII. Desirable properties include: a di-nuclear metal binding site which provides ligands for bivalent metals, a hydrophobic pocket at the dimer interface which can bind a photosensitive porphyrin and presence of tyrosine residues proximal to the bound cofactors, which can be utilised as efficient electron-tunnelling intermediates. Light-induced electron transfer from proximal tyrosine residues to the photo-oxidised ZnCe6(•+), in the modified BFR reconstituted with both ZnCe6 and Mn(II), is presented. Three site-specific tyrosine variants (Y25F, Y58F and Y45F) were made to localise the redox-active tyrosine in the engineered system. The results indicate that: presence of bound Mn(II) is necessary to observe tyrosine oxidation in all BFR variants; Y45 the most important tyrosine as an immediate electron donor to the oxidised ZnCe6(•+) and that Y25 and Y58 are both redox-active in this system, but appear to function interchangebaly. High-resolution (2.1Å) crystal structures of the tyrosine variants show that there are no mutation-induced effects on the overall 3-D structure of the protein. Small effects are observed in the Y45F variant. Here, the BFR-RC represents a protein model for artificial photosynthesis.
authors.affiliation: Building 134, Linnaeus Way, Research School of Biology, The Australian National University, ACT 0200, Australia. Electronic address: kastoori.hingorani@anu.edu.au.
authors.forename: Kastoori
authors.initials: K
authors.lastname: Hingorani
authors.affiliation: Building 137, Sullivans Creek Road, Research School of Chemistry, The Australian National University, ACT 0200, Australia. Electronic address: ron.pace@anu.edu.au.
authors.forename: Ron
authors.initials: R
authors.lastname: Pace
authors.affiliation: Building 134, Linnaeus Way, Research School of Biology, The Australian National University, ACT 0200, Australia.
authors.forename: Spencer
authors.initials: S
authors.lastname: Whitney
authors.affiliation: 724 Sir Ernst Chain Building, South Kensington Campus, Division of Molecular Biosciences, Imperial College London, London SW7 2AZ, United Kingdom.
authors.forename: James W
authors.initials: JW
authors.lastname: Murray
authors.affiliation: Building 137, Sullivans Creek Road, Research School of Chemistry, The Australian National University, ACT 0200, Australia.
authors.forename: Paul
authors.initials: P
authors.lastname: Smith
authors.affiliation: Building 134, Linnaeus Way, Research School of Biology, The Australian National University, ACT 0200, Australia.
authors.forename: Mun Hon
authors.initials: MH
authors.lastname: Cheah
authors.affiliation: Building 134, Linnaeus Way, Research School of Biology, The Australian National University, ACT 0200, Australia.
authors.forename: Tom
authors.initials: T
authors.lastname: Wydrzynski
authors.affiliation: Building 134, Linnaeus Way, Research School of Biology, The Australian National University, ACT 0200, Australia.
authors.forename: Warwick
authors.initials: W
authors.lastname: Hillier
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D001483:Base Sequence; D003573:Cytochrome b Group / Q000737:chemistry / Q000378:metabolism*; D017931:DNA Primers; D004578:Electron Spin Resonance Spectroscopy; D005293:Ferritins / Q000737:chemistry / Q000378:metabolism*; D008958:Models, Molecular; D010084:Oxidation-Reduction; D010777:Photochemistry; D010788:Photosynthesis; D016133:Polymerase Chain Reaction; D015202:Protein Engineering; D014443:Tyrosine / Q000737:chemistry*
chemical_list: D001426:Bacterial Proteins; D003573:Cytochrome b Group; D017931:DNA Primers; D014443:Tyrosine; D005293:Ferritins; C018032:bacterioferritin
keywords: Artificial photosynthesis; Bacterioferritin; Electron transfer; Photosystem II; Protein engineering; Tyrosine oxidation