Elucidating Photochemical Pathways of Tyrosine Oxidation in an Engineered Bacterioferritin ‘Reaction Centre’
Kastoori Hingorani A B , Brendon Conlan A , Warwick Hillier A and Tom Wydrzynski A BA Research School of Biology, Building 46, Australian National University, Canberra, ACT 0200, Australia.
B Corresponding authors. Email: kastoori.hingorani@anu.edu.au; tom.wydrzynski@anu.edu.au
Australian Journal of Chemistry 62(10) 1351-1354 https://doi.org/10.1071/CH09264
Submitted: 4 April 2009 Accepted: 15 July 2009 Published: 13 October 2009
Abstract
Photosystem II (PSII) is the chlorophyll/protein complex in green plants that catalyzes the oxidation of water to molecular oxygen. We have utilized bacterioferritin (BFR), an iron storage protein found in Escherichia coli, as a protein scaffold to build in PSII cofactors in a simpler in vitro model system. Previously, we have shown that the native heme in BFR can be replaced with the chlorophyll analog zinc-chlorin (ZnCe6) and that the intrinsic di-iron site can bind two manganese ions. Upon flash excitation of the ZnCe6 modified BFR, not only is the dinuclear manganese complex oxidized but also a tyrosine residue. There are seven tyrosine residues in each BFR monomeric subunit. We mutated the three tyrosine residues within electron tunnelling distance of the ZnCe6. Here we present evidence based on electron paramagnetic resonance and fluorescence spectroscopy that one is not oxidized while the other two seem to be oxidized in parallel. Localization of this photoactive tyrosine is the first step in creating a linear electron flow in BFR like in PSII.
Acknowledgements
The authors would like to thank Dr Paul Smith for his guidance in using EPR and Sebastian Olenyi for his assistance in creating vector constructs of tyrosine mutants. We would like to acknowledge financial support from the Australian Research Council (DP.0770149).
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