Characterization of light harvesting components and modified amino acids of photosystem II

Oxygenic photosynthesis by plants, algae and cyanobacteria converts solar energy into chemical energy. The released oxygen maintains oxygen in the earth's atmosphere. Photosynthetic electron transport is driven by photosystems I and II. Photosystem II oxidizes water to molecular oxygen, and is the subject of this thesis. This thesis focuses on two topics: light harvesting proteins and modified amino acids of photosystem II.; Research presented in this thesis characterizes light harvesting proteins in a commonly used photosystem II preparation. Tryptic digestion, liquid chromatography, tandem mass spectrometry, and database searching is utilized to identify peptides derived from photosystem II associated light harvesting proteins, Lhcb1–6. This work identifies a sequence variation that has not been previously reported, as well as the presence of two distinct Lhcb1 and two distinct Lhcb4 proteins.; This dissertation research has also revealed unexpected chemical groups at the catalytic site for water oxidation. Evidence for covalent adducts between 14C-amines and PSII subunits are presented. It is also demonstrated that PSII oxidatively deaminates primary amines. The sites of amine labeling and oxidation are shown to be at or near the catalytic site for water oxidation. These results suggest that PSII contains carbonyl containing post-translationally modified amino acids within the oxygen-evolving complex, and that at least one of the modified amino acids is redox-active. These modified amino acids may participate directly in the water oxidation process or may function indirectly by influencing the oxidation potential of the active site manganese atoms. Also, these modified amino acids may be important in regulation, assembly, or turnover of the complex.; Peptide mapping of 14C-amine and phenylhydrazine labeled CP47 using cyanogen bromide, endoproteinase glu-c, trypsin, Edman degradation and tandem mass spectrometry is presented. These data suggest that the modified amino acid is within loop E of the CP47 subunit, which has been shown to be close to or within the oxygen-evolving complex. Furthermore, tandem mass spectra that identify CP47 peptides derivatized with biotin linked hydrazides are presented. These data provide evidence for a modified aspartate in loop E of CP47. This putative modified amino acid, aspartyl aldehyde, constitutes a novel protein modification.