Highly oriented photosynthetic reaction centers generate a proton gradient in synthetic protocells

Significance The photosynthetic reaction center (RC), an integral membrane protein at the core of bioenergetics of all autotrophic organisms, has been reconstituted in the membrane of giant unilamellar vesicles (RC@GUV) by retaining the physiological orientation at a very high percentage (90 ± 1%). Owing to this uniform orientation, it has been possible to demonstrate that, under red-light illumination, photosynthetic RCs operate as nanoscopic machines that convert light energy into chemical energy, in the form of a proton gradient across the vesicle membrane. This result is of great relevance in the field of synthetic cell construction, proving that such systems can easily transduce light energy into chemical energy eventually exploitable for the synthesis of ATP.