Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 107, Issue 21, Pages 9650-9655Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1000187107
Keywords
cyanobacteria; energy conversion; proinhibition; photosynthesis; protein engineering
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Funding
- Israel Science Foundation BIKURA [1046/06]
- Israel Ministry of Science
- Technion V.P.R.
- Israel-Mexico Energy Research Fund
- Phyllis and Joseph Gurwin Fund
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The initial steps of oxygenic photosynthetic electron transfer occur within photosystem II, an intricate pigment/protein transmembrane complex. Light-driven electron transfer occurs within a multi-step pathway that is efficiently insulated from competing electron transfer pathways. The heart of the electron transfer system, composed of six linearly coupled redox active cofactors that enable electron transfer from water to the secondary quinone acceptor Q(B), is mainly embedded within two proteins called D1 and D2. We have identified a site in silico, poised in the vicinity of the Q(A) intermediate quinone acceptor, which could serve as a potential binding site for redox active proteins. Here we show that modification of Lysine 238 of the D1 protein to glutamic acid (Glu) in the cyanobacterium Synechocystis sp. PCC 6803, results in a strain that grows photautotrophically. The Glu thylakoid membranes are able to perform light-dependent reduction of exogenous cytochrome c with water as the electron donor. Cytochrome c photoreduction by the Glu mutant was also shown to significantly protect the D1 protein from photodamage when isolated thylakoid membranes were illuminated. We have therefore engineered a novel electron transfer pathway from water to a soluble protein electron carrier without harming the normal function of photosystem II.
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