Specialized Roles of Plasma and Thylakoid Membranes
A small region of two adjacent closely appressed membranes that cannot accommodate phycobilisomes is presented undulating freely in the cytoplasm, and the corresponding interthylakoidal distances. From q1 to q4 NSE samples a larger distance (57 Å–175 Å) within the interthylakoidal space and different relaxation behavior is observed. The excess of protons (H + ) in the thylakoid lumen results in restricted membrane dynamics observed during light. At dark, H + pressure is alleviated by chemiosmosis and the membranes undulate freely resulting in higher relaxation rates and excess dynamics. Purple feature is the ATP-Synthase responsible for moving down the electrochemical gradient. The center-to-center distance of a membrane pair corresponds to SANS correlation peaks for closely appressed membranes in Fig. 2 (100 Å–180 Å).
Cyanobacteria are photosynthetic microbes with highly differentiated membrane systems. In order to identify the components of the plasma membrane (PM) and thylakoid membrane (TM), we used a sensitive LC-MS/MS based analysis pipeline, which resulted in the identification of 635 proteins with significantly different localizations across PM and TM in Synechocystis sp. PCC 6803. The overall composition of PM was characterized by proteins involved in transport, secretion, and trafficking, whereas the TM protein composition described a specialized membrane system dedicated to the energetics of electron transport. This specialization highlights the distinct roles these membrane systems have in cyanobacterial cellular metabolism. One of the proteins localized to the TM, the thioredoxin-like (Trx) protein Slr1796, was found to be involved in regulating photosystem stoichiometry. The deletion of Slr1796 resulted in a dramatic decrease in cellular photosystem I (PSI) content, while PSII activity was unchanged. These analyses revealed important findings about cyanobacterial membrane systems and photosystem regulation.
