Dynamic pH‐induced conformational changes of the PsbO protein in the fluctuating acidity of the thylakoid lumen

Abstract

The PsbO protein is an essential extrinsic subunit of photosystem II, the pigment–protein complex responsible for light‐driven water splitting. Water oxidation in photosystem II supplies electrons to the photosynthetic electron transfer chain and is accompanied by proton release and oxygen evolution. While the electron transfer steps in this process are well defined and characterized, the driving forces acting on the liberated protons, their dynamics and their destiny are all largely unknown. It was suggested that PsbO undergoes proton‐induced conformational changes and forms hydrogen bond networks that ensure prompt proton removal from the catalytic site of water oxidation, i.e. the Mn4CaO5 cluster. This work reports the purification and characterization of heterologously expressed PsbO from green algae Chlamydomonas reinhardtii and two isoforms from the higher plant Solanum tuberosum (PsbO1 and PsbO2). A comparison to the spinach PsbO reveals striking similarities in intrinsic protein fluorescence and CD spectra, reflecting the near‐identical secondary structure of the proteins from algae and higher plants. Titration experiments using the hydrophobic fluorescence probe ANS revealed that eukaryotic PsbO proteins exhibit acid–base hysteresis. This hysteresis is a dynamic effect accompanied by changes in the accessibility of the protein's hydrophobic core and is not due to reversible oligomerization or unfolding of the PsbO protein. These results confirm the hypothesis that pH‐dependent dynamic behavior at physiological pH ranges is a common feature of PsbO proteins and causes reversible opening and closing of their β‐barrel domain in response to the fluctuating acidity of the thylakoid lumen.

A study on the secondary structure of the metalloregulatory protein CueR: effect of pH, metal ions and DNA

“…Conformational changes within a narrow pH range observed for CueR are not unique, but rather rare among proteins, and are suggested to be attributed to a single residue (de)protonation. Such phenomena may trigger or influence various biochemical processes including the formation of β-sheet rich structures that are prone to aggregation in prion proteins (Alonso et al 2002;Alonso et al 2001;Kelly 1998;Langella et al 2004), metal ion or ligand binding of proteins (Cabra et al 2006;Kun et al 2009;Leloup et al 2017;Yoo and Albanesi 1991), interaction with membranes (Bañares- Hidalgo et al 2014;Harrison et al 2013;Kannan et al 2019;Nguyen et al 2008;Puhar et al 2004) or influencing enzyme activities (Carius et al 2019;Di Russo et al 2012;Georgieva et al 2008;Mishra et al 2015;Nar et al 1991;Yeo et al 2014). Nevertheless, a similar observation has not been reported so far for metalloregulatory proteins.…”

Ascorbate inactivates the oxygen‐evolving complex in prolonged darkness

“…Regarding the reason for the altered binding of the extrinsic proteins in the dark, the question remains. PSBO was shown to undergo conformational changes upon luminal pH changes (Carius et al, 2019) and it has been proposed that loss of pmf during extended dark periods may result in Ca 2+ loss from the lumen, which may have a direct or indirect effect on OEC (Sai & Johnson, 2002).…”

Optimisation of Protein Extraction from Selenium-Enriched Brassicaceae Leaves

“…Additionally, the globulin fraction exhibited a prominent band at 23 kDa, whereas the glutelin fraction displayed a faint band around 30 kDa. The prolamin fraction appeared to contain a lower proportion of LSU, with an additional band emerging at 27 kDa, possibly representing the light-harvesting chlorophyll a/b protein complex of photosystem II (LHCPII) (Carius et al, 2019;Onaizi et al, 2007). Besides, there was a limited migration of prolamin fraction through the gel, leading to their retention at the loading zone.…”