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Tiny Protein Ends Photosynthesis

In developing solar cells that mimic nature, scientists discover a molecular showstopper

Three-dimensional images of photosynthetic membranes of Rhodobacter sphaeroides. Contrast represents the measured height of features. (Top) Membrane patch from the natural bacteria. (Bottom) Membrane patch from the bacteria without the PufX protein. Single RC-LH1 protein complexes form large rings; LH2 complexes are smaller rings.

Would you buy a television that only worked when the sun was shining? A hair dryer? A dishwasher? The challenge in replacing fossil fuels with solar energy is the intermittent nature of the supply. While the challenge is great, some very small life forms have proven to be up to the task. A bacterium called Rhodobacter sphaeroides efficiently traps sunlight and creates fuels using photosynthesis. Protein-based scaffolding inside the cell holds pigments that capture sunlight, which is turned into fuel for the bacteria. Scientists are studying the bacteria’s pigment-protein molecules to mimic their light-harvesting efficiency. They discovered that a small protein, named “PufX,” plays a critical role in photosynthesis in this species. When genetically removed, the bacterium rearranges the internal light-absorbing membranes where photosynthesis occurs. Understanding these proteins could be a fundamental breakthrough to creating solar cells that produce fuels. This research was done by the Photosynthetic Antenna Research Center, led by Washington University in St. Louis.

References:

Adams PG, DJ Mothersole, IW Ng, JD Olsen, and CN Hunter. 2011. “Monomeric RC–LH1 Core Complexes Retard LH2 Assembly and Intracytoplasmic Membrane Formation in PufX-Minus Mutants of Rhodobacter sphaeroides.” Biochimica et Biophysica Acta 1807(9), 1044-1055. DOI: 10.1016/j.bbabio.2011.05.019.

Ratcliffe EC, RB Tunnicliffe, IW Ng, PG Adams, P Qian, K Holden-Dye, MR Jones, MP Williamson, and CN Hunter. 2011. “Experimental Evidence that the Membrane-Spanning Helix of PufX Adopts a Bent Conformation that Facilitates Dimerisation of the Rhodobacter sphaeroides RC-LH1 Complex Through N-Terminal Interactions.” Biochimica et Biophysica Acta 1807(1), 95-107. DOI: 10.1016/j.bbabio.2010.10.003.