The importance of protein-protein interactions for optimising oxygen activity in photosystem II: reconstitution with a recombinant thioredoxin--manganese stabilising protein

Thomas John Wydrzynski (8 July 1947-16 March 2018)

With this Tribute, we remember and honor Thomas John (Tom) Wydrzynski. Tom was a highly innovative, independent and committed researcher, who had, early in his career, defined his life-long research goal. He was committed to understand how Photosystem II produces molecular oxygen from water, using the energy of sunlight, and to apply this knowledge towards making artificial systems. In this tribute, we summarize his research journey, which involved working on 'soft money' in several laboratories around the world for many years, as well as his research achievements. We also reflect upon his approach to life, science and student supervision, as we perceive it. Tom was not only a thoughtful scientist that inspired many to enter this field of research, but also a wonderful supervisor and friend, who is deeply missed (see footnote*).

Structural and mechanistic investigations of photosystem II through computational methods

The advent of oxygenic photosynthesis through water oxidation by photosystem II (PSII) transformed the planet, ultimately allowing the evolution of aerobic respiration and an explosion of ecological diversity. The importance of this enzyme to life on Earth has ironically been paralleled by the elusiveness of a detailed understanding of its precise catalytic mechanism. Computational investigations have in recent years provided more and more insights into the structural and mechanistic details that underlie the workings of PSII. This review will present an overview of some of these studies, focusing on those that have aimed at elucidating the mechanism of water oxidation at the CaMn₄ cluster in PSII, and those exploring the features of the structure and dynamics of this enzyme that enable it to catalyse this energetically demanding reaction. This article is part of a Special Issue entitled: Photosystem II.

The evolution of Photosystem II: insights into the past and future

This article attempts to address the molecular origin of Photosystem II (PSII), the central component in oxygenic photosynthesis. It discusses the possible evolution of the relevant cofactors needed for splitting water into molecular O2 with respect to the following functional domains in PSII: the reaction center (RC), the oxygen evolving complex (OEC), and the manganese stabilizing protein (MSP). Possible ancestral sources of the relevant cofactors are considered, as are scenarios of how these components may have been brought together to produce the intermediate steps in the evolution of PSII. Most importantly, the driving forces that maintained these intermediates for continued adaptation are considered. We then apply our understanding of the evolution of PSII to the bioengineering of a water oxidizing catalyst for utilization of solar energy.

Importance of a single disulfide bond for the PsbO protein of photosystem II: protein structure stability and soluble overexpression in Escherichia coli

PsbO protein is an important constituent of the water-oxidizing complex, located on the lumenal side of photosystem II. We report here the efficient expression of the spinach PsbO in E. coli where the solubility depends entirely on the formation of the disulfide bond. The PsbO protein purified from a pET32 system that includes thioredoxin fusion is properly folded and functionally active. Urea unfolding experiments imply that the reduction of the single disulfide bridge decreases stability of the protein. Analysis of inter-residue contact density through the PsbO molecule shows that Cys51 is located in a cluster with high contact density. Reduction of the Cys28-Cys51 bond is proposed to perturb the packing interactions in this cluster and destabilize the protein as a whole. Taken together, our results give evidence that PsbO exists in solution as a compact highly ordered structure, provided that the disulfide bridge is not reduced.

Structural and functional aspects of the MSP (PsbO) and study of its differences in thermophilic versus mesophilic organisms

The Manganese Stabilizing Protein (MSP) of Photosystem II (PSII) is a so-called extrinsic subunit, which reversibly associates with the other membrane-bound PSII subunits. The MSP is essential for maximum rates of O(2) production under physiological conditions as stabilizes the catalytic [Mn(4)Ca] cluster, which is the site of water oxidation. The function of the MSP subunit in the PSII complex has been extensively studied in higher plants, and the structure of non-PSII associated MSP has been studied by low-resolution biophysical techniques. Recently, crystal structures of PSII from the thermophilic cyanobacterium Thermosynechococcus elongatus have resolved the MSP subunit in its PSII-associated state. However, neither any crystal structure is available yet for MSP from mesophilic organisms, higher plants or algae nor has the non-PSII associated form of MSP been crystallized. This article reviews the current understanding of the structure, dynamics, and function of MSP, with a particular focus on properties of the MSP from T. elongatus that may be attributable to the thermophilic ecology of this organism rather than being general features of MSP.

Recollections of Thomas John Wydrzynski

In appreciation of his contribution to the Photosystsem II research and commemoration of the book Photosystem II: The Light-Driven Water-Plastoquinone Oxido-Reductase, co-edited with Kimiyuki Satoh, I present here some of my recollections of Thomas John Wydrzynski and by several others with whom he has associated over the years at Urbana (Illinois), Berkeley (California), Standard Oil Company-Indiana (Illinois), Berlin (Germany), Gothenburg (Sweden), and Canberra (Australia). We not only recognize him for his unique career path in Photosystem II research, but also for his qualities as a collaborative scientist working on the only system on Earth that has the ability to oxidize water to molecular oxygen using the energy of sunlight.