The conversion of light into chemical energy by plants and photosynthetic microorganisms is one of the most important processes in nature, removing climate-damaging CO2 from the atmosphere. Protein complexes, so-called photosystems, play the key role in this process. An international research team from Ruhr-Universität Bochum (RUB), the Max Planck Institutes of Biochemistry and Biophysics, the Center for Synthetic Microbiology (SYNMIKRO) and the Chemistry Department at Philipps Universität Marburg, the University of Illinois Urbana-Champaign, U.S., and Université Paris-Saclay, France, shed light for the first time on the structure and function of a transition state in the synthesis of photosystem II. The study was published online on 12 April 2021 in the journal Nature Plants.