The light-harvesting core antenna (LH1) and the reaction centre (RC) of purple photosynthetic bacteria form a supramolecular complex (LH1—RC) to use sunlight energy in a highly efficient manner. Niwa et al. [1—4] report the first near-atomic structure of a LH1—RC complex, namely that of a Ca2+-bound complex from Thermochromatium tepidum. The RC is surrounded by 16 heterodimers of the LH1 αβ-subunit that form a completely closed structure. The Ca2+ ions are located at the periplasmic side of LH1. Thirty-two bacteriochlorophyll a and sixteen spirilloxanthin molecules in the LH1 ring form an elliptical assembly.