Skip to content

Information for students, faculty and staff regarding COVID-19. (Updated: 15 April 2021)

printicon

The role of some of the extrinsic proteins in the oxygen evolution mechanism

Research project Plants produce oxygen to the atmosphere. Oxygen is important for most living organisms.

Photosystem II (PSII) uses the sunlight to split water, an energetically unfavorable reaction where electrons and protons are extracted from water and oxygen is released as a by-product. Understanding this process is crucial for the future development of clean, renewable and unlimited energy sources. We have been focusing on the role of two lumenal proteins, PsbO and Cah3, in the water oxidation process. Data is presented supporting the hypothesis that bicarbonate acts as a proton acceptor in the water splitting process in PSII and that the lumenal carbonic anhydrase, Cah3, supplies bicarbonate required for this function. On the other hand, the PsbO protein, an important constituent of the water-oxidizing complex, however, has an unknown function.

Head of project

Göran Samuelsson
Professor emeritus
E-mail
Email

Project overview

Project period:

2008-01-22 2009-12-31

Funding

Finansår , 2005, 2006, 2007, 2008

huvudman: Göran Samuelsson, finansiär: Vetenskapsrådet, y2005: 500, y2006: 500, y2007: 500, y2008: 500,

huvudman: Göran Samuelsson/institutionen gemensamt, finansiär: STINT, y2005: , y2006: 600, y2007: , y2008: ,

Participating departments and units at Umeå University

Department of Plant Physiology, Faculty of Science and Technology

Research area

Biological sciences, Botany

Project description

The solar energy accumulated by photosynthesis over billions of years is the sole source of energy available on Earth. Photosystem II (PSII) uses the sunlight to split water, an energetically unfavorable reaction where electrons and protons are extracted from water and oxygen is released as a by-product. Understanding this process is crucial for the future development of clean, renewable and unlimited energy sources, which can use sunlight to split water and produce hydrogen and electricity. In order to do so we need to understand how this is solved in plants.

We were focusing on the role of two lumenal proteins associated with the thylakoid membrane PsbO and Cah3, in the water oxidation process. Convincing evidences have been presented supporting the hypothesis that bicarbonate acts as a proton acceptor in the water splitting process in PSII and the lumenal carbonic anhydrase, Cah3, supplies bicarbonate required for this function. The PsbO protein, an important constituent of the water-oxidizing complex, however, its function is still unknown. The PsbO protein undergoes a pH dependent conformational change that in turn influences its capacity to bind calcium and manganese, forming a catalytic Mn4Ca cluster in PSII. We propose that light-induced structural dynamics of the PsbO is of functional relevance for the regulation of proton release and for forming a proton sensing - proton transporting pathway. The cluster of conserved glutamic and aspartic acid residues in the PsbO protein acts as buffering antennae providing efficient acceptors of protons derived from substrate water molecules. Both proteins, Cah3 and PsbO have a conserved S-S bridge, required for proper folding and activity; therefore they are potential targets for red-ox regulation in lumen.