Extra Chlorophyll Helps Bacteria Photosynthesize

A key photosynthesis protein in certain bac teria contains eight bacteriochlorophyll molecules—one more than previously realized (Biochemistry, DOI: 10.1021/bi200239k). The additional compound is critical to understanding and modeling exactly how the bacteria turn sunlight into chemical energy. In green sulfur bacteria, the photosynthetic machinery is made up of an antenna complex that acts like a satellite dish to gather energy from sunlight, a reaction center that does electron-transfer chemistry, and the FMO protein (trimer shown) that acts like a wire to connect the two. Energy flows through seven bacteriochlorophyll compounds in FMO through a delocalized, quantum coherence mechanism, but researchers didn’t understand how energy got from the antenna complex into FMO. In new work, Robert E. Blankenship, Michael L. Gross, and colleagues at Washington University in St. Louis used mass spectrometry to demonstrate that a previously unidentified bacteriochlorophyll (shown in pink) likely provides the missing link. The compound probably resides on the FMO surface in an area that would interface with the antenna complex.