Multi-way fluorescence based investigation of conformation changes in photosystem II around nanosized manganese oxide as an artificial enzyme

Oxygenic photosynthesis is a physical-chemical process which is utilized by the plants, algae and cyanobacteria using light energy to build carbohydrates from carbon dioxide and water, releasing molecular oxygen into the atmosphere. The production of oxygen is related to photosystem II (PSII), which is composed of a Mn-Ca cluster includes D1 and D2 polypeptides [1]. The conformation of proteins in photosystem II can be changed under different conditions. These changes are effective on different states of structure, and are found important for understanding protein functions [2]. One of techniques that was used for monitoring protein conformational changes is the fluorescence spectroscopy. Similar to other proteins, fluorescence characterization of PSII is primarily due to existing tryptophan (Trp), tyrosine (Tyr) and phenylalanine (Phe) amino-acids. Zero- and first-order PSII fluorescence measurements were used in different studies [3]. Excitation–emission Matrix (EEM) fluorescence spectroscopy is a rather fast and inexpensive analytical technique with selectivity and high sensitivity that due to use of an additional mode in EEM fluorescence and the second order advantage, the potency for resolution of overlapped spectra is improved. PARAFAC is the most generally applied second-order algorithm to decompose these trilinear EEM data. [4]. In this study, 3D-fluorescence spectroscopy and PARAFAC were used to characterize and differentiate spectral variations of three various samples, as a function of pH. Change in pH influences the PSII conformation at the tertiary structure level, changes the surface amino acids. This variation of position can be detected via the fluorescence spectral changes of the PSII proteins as a function of pH [3]. Different variations of profiles in the presence and absence of nano-cluster was applied to distinguish the presence of clusters in the proteins using low-cost, sensitive and rapid spectrofluorimetry.