Photosynthesis converts solar energy to chemical energy by means of two large
pigment-protein complexes: photosystem I (PSI) and photosystem II (PSII). In
higher plants, the PSI core is surrounded by a large light-harvesting complex I
(LHCI) that captures sunlight and transfers the excitation energy to the core
with extremely high efficiency. We report the structure of PSI-LHCI, a
600-kilodalton membrane protein supercomplex, from Pisum sativum (pea) at a
resolution of 2.8 angstroms. The structure reveals the detailed arrangement of
pigments and other cofactors—especially within LHCI—as well as numerous
specific interactions between the PSI core and LHCI. These results provide a
firm structural basis for our understanding on the energy transfer and
photoprotection mechanisms within the PSI-LHCI supercomplex.
