Abstact

During oxygenic photosynthesis, photosystem II (PSII) uses light energy for oxidizing water and reducing plastoquinone. It is susceptible to photodamage, and the damaged PSII is repaired through a sophisticated biological process assisted by numerous auxiliary proteins. Here we report the cryogenic electron microscopy structures of four PSII-repair complexes from Chlamydomonas reinhardtii associated with the Thylakoid Enriched Fraction 30 (TEF30, an orthologue of plant MET1) protein-namely, a TEF30-PSII core monomer (TEF30-C), two types of TEF30-PSII core dimers (types I and II, TEF302-C2-I and TEF302-C2-II) and a TEF30-C2S-type PSII-LHCII supercomplex (TEF30-C2S; S, strongly associated light-harvesting complex II trimer). TEF30 mediates the assembly of CP43 with the RC47 module by clamping on the stromal surfaces and prevents the premature association of peripheral antennae with PSII-C. In the transition from TEF302-C2-I to TEF302-C2-II, TEF30-C2S and mature C2S2, one PSII core slides along the dimerization interface against the adjacent one by 22-35 Å, generating a zigzagged surface for accommodating the peripheral antennae. These results suggest that the PSII repair process undergoes multiple TEF30-mediated intermediate states to form intact PSII-LHCII supercomplexes.