Abstract:
Photosystem I (PSI) and photosystem II (PSII) represent reaction centre complexes of oxygenic phototrophs which perform the photochemical energy conversion. While the high resolution structures of both complexes are known for large number of organisms, many details in their biogenesis process remain unclear. According to widely accepted modular model (small PSII subunits and pigments associate with large pigment-binding proteins prior to their joining into the complex) the biogenesis of PSII starts with modules of the central D1 and D2 subunits forming the reaction center complex (RCII). Characterization of both modules and RCII including its high resolution structure will be presented. Later in the process, modules of inner antennas CP47 and CP43 associate with RCII and then lumenal subunits and CaMn4O5 cluster are attached to form the final functional complex that dimerizes. Unlike PSII, PSI is believed to start with formation of a heterodimer of the two largest PSI protein components PsaA and PsaB (RCI), which afterwards attach stromal subunits and finally at the end of biogenesis the remaining small transmembrane subunits associate with RCI. Our recent isolation and characterization of individual of FLAG-tagged PsaA and PsaB proteins showed that FLAG-PsaA mostly forms a highly pigmented homodimer containing stabilizing PsaK subunit, which can be considered a prototype of the ancient PSI-like homodimeric reaction centre. In contrast, the isolated monomeric FLAG- PsaB contains only a small number of associated Chls. In the absence of cytoplasmic PsaC the accumulated FLAG-PSI complex lacks all cytoplasmic subunits while all transmembrane ones are present. All these results are in agreement with modular principle of PSI assembly similar to that previously verified for PSII, during which the small transmembrane subunits associate with PsaA and PsaB prior to heterodimerization and independently of cytoplasmic subunits.

Bio:
Dr. Josef Komenda graduated in biochemistry from Charles University in Prague in 1987 and went on to earn a PhD in microbiology from the Institute of Microbiology in Prague in 1993. Following his doctorate, he broadened his research experience with a year as a research assistant at Imperial College London in the Department of Biochemistry. Currently, he serves as a senior researcher at the Institute of Microbiology in Třeboň and holds a professorship at the Faculty of Science, University of South Bohemia in České Budějovice (Budweis), Czech Republic. Dr. Komenda actively collaborates with research groups across the UK, Germany, Austria, and Saudi Arabia, including the team led by Andreas Naschberger. His research primarily focuses on the biogenesis and quality control of photosynthetic membrane complexes, contributing significantly to the understanding of photosynthesis and cellular processes in various organisms.