The Use of Advanced Mass Spectrometry to Dissect the Life-Cycle of Photosystem II

Abstract

Photosystem II (PSII) is a photosynthetic membrane-protein complex that undergoes an intricate, tightly regulated cycle of assembly, damage, and repair. The available crystal structures of cyanobacterial PSII are an essential foundation for understanding PSII function, but nonetheless provide a snapshot only of the active complex. To study aspects of the entire PSII life-cycle, mass spectrometry (MS) has emerged as a powerful tool that can be used in conjunction with biochemical techniques. In this article, we present the MS-based approaches that are used to study PSII composition, dynamics, and structure, and review the information about the PSII life-cycle that has been gained by these methods. This information includes the composition of PSII subcomplexes, discovery of accessory PSII proteins, identification of post-translational modifications and quantification of their changes under various conditions, determination of the binding site of proteins not observed in PSII crystal structures, conformational changes that underlie PSII functions, and identification of water and oxygen channels within PSII. We conclude with an outlook for the opportunity of future MS contributions to PSII research.

Tracing the Pathways of Waters and Protons in Photosystem II and Cytochrome c Oxidase

“…There are several physical methods that can help follow the pathway of water, O 2 , and protons [123,128,129,132]. Radiolytic footprinting can trace the residues surrounding water channels and also buried waters [140,141]. Exposure of the protein to X-rays produces OH• which will oxidatively modify nearby amino acids.…”

Mass spectrometry-based cross-linking study shows that the Psb28 protein binds to cytochrome b 559 in Photosystem II

“…PSII samples were cross-linked using a 1:1 mixture of unlabeled BS 3 and BS 3 labeled with 12 deuteriums (Creative Molecules) for 50 min in the dark at room temperature, at a cross-linker:PSII molar ratio of 50:1, 100:1, and 300:1, with PSII sample containing 1 or 2 μg Chl a. After quenching, samples were precipitated, resuspended, and digested with lysyl endopeptidase (LysC), then trypsin.…”

“…Crystal structures of the active complex from thermophilic cyanobacteria are available (1,4,5), but they do not capture the transient interactions of the various accessory proteins that regulate the life cycle by binding exclusively to intermediate subcomplexes. Nevertheless, significant progress has been made in characterizing these intermediates through complementary use of genetic modification, biochemical analysis, and mass spectrometry (MS) (3,(6)(7)(8)(9). Although crystal structures of assembly intermediate complexes are not available, the binding site of one accessory protein, Psb27, on the luminal surface of PSII has been determined by chemical cross-linking and MS (10,11).…”

“…3). The assembly occurs stepwise via multiple transient intermediate complexes that are difficult to study because of their low abundance, relatively short lifetimes, and heterogeneity.…”

A Novel Antenna Protein Complex in the Life Cycle of Cyanobacterial Photosystem II

“…CP47 and CP43 are, however, more long lived (15, 17). This damage leads to partial disassembly of PSII, replacement of each damaged subunit with a new copy, and reassembly of PSII, in an intricate process known as the PSII repair cycle (14, 18, 19) (Fig. S1).…”