Adapting to the right light: In plants, photosystem II is the first protein complex in the machinery that converts sunlight into chemical energy. It comprises antennae complexes (LHCIIs), which collect the light energy, and a dimeric core that contains the reaction center where water is split into oxygen and protons. Su et al. report cryo-electron microscopy structures of a supercomplex consisting of the dimeric core, two strongly bound LHCIIs, and two moderately bound LHCIIs (see the Perspective by Croce and van Amerongen). Under high-light conditions, the moderately bound LHCIIs might detach to down-regulate the efficiency of light harvesting and prevent damage. Science , this issue p. 815 ; see also p. 752

Antenna switches partners in the shade: A cloudy day or an overshadowing tree causes fluctuations in light that can throw off the balance of energy flow in plant photosystems I and II (PSI and PSII). Pan et al. solved structures of PSI bound to two light-harvesting complexes (LHCs). One LHC is permanently associated with PSI. The other LHC delivers light energy to PSII under optimal conditions but can switch to a PSI-associated state after phosphorylation by a kinase that senses the redox environment of the chloroplast. The movement of LHCs between the photosystems helps maintain even energy flux. Two chlorophyll-containing subunits are visible in the structure that connect the PSI core to each LHC. Science , this issue p. 1109

Global emergencies caused by the severe acute respiratory syndrome coronavirus (SARS-CoV), Middle-East respiratory syndrome coronavirus (MERS-CoV) and SARS-CoV-2 significantly endanger human health. The spike (S) glycoprotein is the key antigen and its conserved S2 subunit contributes to viral entry by mediating host-viral membrane fusion. However, structural information of the post-fusion S2 from these highly pathogenic human-infecting coronaviruses is still lacking. We used single-particle cryo-electron microscopy to show that the post-fusion SARS-CoV S2 forms a further rotated HR1-HR2 six-helix bundle and a tightly bound linker region upstream of the HR2 motif. The structures of pre- and post-fusion SARS-CoV S glycoprotein dramatically differ, resembling that of the Mouse hepatitis virus (MHV) and other class I viral fusion proteins. This structure suggests potential targets for the development of vaccines and therapies against a wide range of SARS-like coronaviruses.