PsbU Provides a Stable Architecture for the Oxygen-Evolving System in Cyanobacterial Photosystem II

Abstract

PsbU is a lumenal peripheral protein in the photosystem II (PS II) complex of cyanobacteria and red algae. It is thought that PsbU is replaced functionally by PsbP or PsbQ in plant chloroplasts. After the discovery of PsbP and PsbQ homologues in cyanobacterial PS II [Thornton et al. (2004) Plant Cell 16, 2164-2175], we investigated the function of PsbU using a psbU deletion mutant (DeltaPsbU) of Synechocystis 6803. In contrast to the wild type, DeltaPsbU did not grow when both Ca2+ and Cl- were eliminated from the growth medium. When only Ca2+ was eliminated, DeltaPsbU grew well, whereas when Cl- was eliminated, the growth rate was highly suppressed. Although DeltaPsbU grew normally in the presence of both ions under moderate light, PS II-related disorders were observed as follows. (1) The mutant cells were highly susceptible to photoinhibition. (2) Both the efficiency of light utilization under low irradiance and the chlorophyll-specific maximum rate of oxygen evolution in DeltaPsbU cells were 60% lower than those of the wild type. (3) The decay of the S2 state in DeltaPsbU cells was decelerated. (4) In isolated PS II complexes from DeltaPsbU cells, the amounts of the other three lumenal extrinsic proteins and the electron donation rate were drastically decreased, indicating that the water oxidation system became significantly labile without PsbU. Furthermore, oxygen-evolving activity in DeltaPsbU thylakoid membranes was highly suppressed in the absence of Cl-, and 60% of the activity was restored by NO3- but not by SO4(2-), indicating that PsbU had functions other than stabilizing Cl-. On the basis of these results, we conclude that PsbU is crucial for the stable architecture of the water-splitting system to optimize the efficiency of the oxygen evolution process.

Samples of cyanobacterium Calothrix sp. ISC 65 collected from oil polluted regions respond to combined effects of salinity, extremely low-carbon dioxide concentration and irradiance

“…Соотношение фотосистем и их характеристики определяли спектрофлуориметром (Inoue-Kashino et al, 2005;Zorz et al, 2015). Для получения спектров поглощения интактных клеток осадок суспендировали в 3 мл реакционного буфера.…”

Ideal Osmotic Spaces for Chlorobionts or Cyanobionts Are Differentially Realized by Lichenized Fungi

“…Steady-state fluorescence emission spectra at 77 K were measured using an H-20 UV monochromator (Jobin Yvon) following the method described previously (Inoue-Kashino et al, 2005).…”

Function of Extrinsic Proteins in Stabilization of the Photosynthetic Oxygen-Evolving Complex

“…In cyanobacteria, PsbU-lacking mutants were capable of photoautotrophic growth in the absence of Ca 2+ or Cl -, but at reduced rates [Shen et al, 1998]. The oxygen-evolving ability was reduced by the removal of PsbU and restored in part by the addition of Cl -but not Ca 2+ , indicating that PsbU regulates Cl -requirement [Inoue-Kashino et al, 2005. Another of its functions is the suppression of light-induced D1 degradation [Inoue-Kashino et al, 2005].…”

“…The oxygen-evolving ability was reduced by the removal of PsbU and restored in part by the addition of Cl -but not Ca 2+ , indicating that PsbU regulates Cl -requirement [Inoue-Kashino et al, 2005. Another of its functions is the suppression of light-induced D1 degradation [Inoue-Kashino et al, 2005]. Protection of the PSII core from reactive oxygen species (ROS) [Balint et al, 2006] has also been proposed.…”