Overall structure of the H. modesticaldum photosynthetic reaction center. The transmembrane helices are shown in gold and red. Light-harvesting “antenna” molecules are colored green, and the electron-transfer chain is colored blue. (Credit: Christopher Gisriel)

Found in muddy soils near hot springs, Heliobacterium modesticaldum is the simplest bacterium known to be able to drive photosynthesis. Its photosynthesis reaction centers are thought to resemble the earliest common ancestor of all photosynthesis complexes, which evolved around three billion years ago. Now, for the first time, a team led by researchers from Arizona State University has obtained a near-atomic resolution (2.2 Å) structure of the membrane protein at the heart of H. modesticaldum’s photosynthetic reaction center using X-ray crystallography data collected at ALS Beamline 8.2.1. The structure gives researchers a new perspective on the early evolution of photosynthesis. Read more in this ALS Science Brief.