Switching sides—Reengineered primary charge separation in the bacterial photosynthetic reaction center

Significance Photosynthetic organisms use pigment–protein complexes called reaction centers (RCs)—effectively nature’s solar cells—to convert the energy of sunlight into charge-separated species that power life processes. Whether from plants, algae, or photosynthetic bacteria, RCs feature 2 quasi-mirror-image arrangements of protein and pigment cofactors. In RCs from purple photosynthetic bacteria, photon-induced electron transfer (ET) reduces the A-branch bacteriopheophytin (BPh) with near-unity quantum yield, while ET to the symmetry-related B-branch BPh is suppressed. Amino acid changes made here in the Rhodobacter sphaeroides RC nearly completely reverse this design. Specifically, we report RCs wherein ET to the B-branch BPh occurs with 90% yield. We draw insight regarding architectural and mechanistic foundations of the primary photon-driven charge-separation events of photosynthesis.