Abstract
Proper biogenesis and maintenance of photosynthetic thylakoid membrane complexes are essential for the photosynthetic light reactions. A thylakoid lumenal protein, Psb27, plays a vital role in assembly or/and maintenance of photosystem II (PSII). In cyanobacteria, it is a small lipoprotein docked to the lumenal side of PSII, and functions in the assembly of the Mn4Ca cluster and in the PSII repair cycle. However, Psb27 from Arabidopsis thaliana is not a lipoprotein, and it is involved in PSII repair and acclimation to fluctuating light stress, suggesting a functional divergence between Arabidopsis Psb27 and cyanobacterial Psb27s. To gain a better understanding of Psb27 from higher plants, we determined the crystal structure of Arabidopsis Psb27 by X-ray crystallography at a resolution of 1.85 Å. The structure of Arabidopsis Psb27 is a four-helix bundle, similar to its orthologues from cyanobacteria. However, there are several structural differences between Arabidopsis Psb27 and cyanobacterial Psb27s concerning the overall molecular shape, the N- and C-terminal structures, and the surface charge. These differences suggest that Psb27 from higher plants and cyanobacteria may function differently.
Highlights
Photosystem II (PSII) is the electron donor of the photosynthetic electron transfer chain, where it catalyzes the lightdriven oxidation of water and the reduction of plastoquinone (Nelson and Yocum 2006; Barber 2006)
Our study suggests that Psb27 proteins from higher plants and cyanobacteria may be involved in the assembly and repair of PSII through different mechanisms
The full length protein of Psb27 from A. thaliana is composed of 174 amino acids (AA), with a 68 AA-long chloroplast targeting peptide at the N-terminus
Summary
Photosystem II (PSII) is the electron donor of the photosynthetic electron transfer chain, where it catalyzes the lightdriven oxidation of water and the reduction of plastoquinone (Nelson and Yocum 2006; Barber 2006). Li Fudong lifudong@ustc.edu.cn structure of Arabidopsis Psb27 is a four-helix bundle, similar to its orthologues from cyanobacteria. The crystal structure reveals major differences between AtPsb27 and cyanobacterial Psb27, with respect to the global molecular shape, the N- and C-terminal structures, and the surface charge.
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