In the quest to harness solar energy for fuel, the Photosynthetic Antenna Research Center studies the highly efficient process of photosynthesis, aiming to create next-generation energy-harvesting devices. PARC researchers showed that altering one small protein completely rearranges the hundreds of other proteins that comprise the light-harvesting network. These studies provide the first clues about the role of protein organization in trapping of solar energy.
Photosynthesis works because groups of thousands of chlorophyll molecules capture photons and funnel the energy to a reaction center, or RC, protein, where conversion to electrical energy occurs. These chlorophylls are attached to proteins, forming light-harvesting, or LH, complexes that sit side-by-side in a membrane a few nanometers thick. Understanding how these LH complexes are arranged and connected in the membrane is critical to photosynthesis.
A photosynthetic bacterium, Rhodobacter sphaeroides, was studied, because it performs similar reactions to plants, but is easier to grow and study. The researchers used an atomic force microscope to create a nanoscale map of a photosynthetic membrane. The AFM images show how bacterial photosynthetic membranes are packed with LH2 complexes that collect solar energy and transfer it to RC complexes surrounded by a dedicated complex called LH1. The very high efficiency of these nanoscale solar energy collectors lies in the size, shape and membrane organization of these complexes.
To find out what would happen if the membrane organization was altered, the team used genetics to disrupt a single, small protein named “PufX,” which is part of the RC-LH1 complex... In two sets of experiments, the protein was either truncated or completely removed. Normally, RC-LH1 complexes are twinned in the membrane, but the loss or shortening of PufX converted them to single complexes and completely reorganized the membranes with a consequent drop in solar energy conversion.
These investigations showed that with the power of genetics and high-resolution microscopy, scientists can explore large-scale disruptions to natural photosynthesis. The more we understand about photosynthesis, the closer we get to realizing its potential in cheap and efficient conversion of solar energy to fuels for us all.
