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.

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.

Project Publications

Zhu, Yuehui, Michelle Liberton, and Himadri B. Pakrasi. “A Novel Redoxin in the Thylakoid Membrane Regulates the Titer of Photosystem I.” Journal of Biological Chemistry (2016): jbc-M116.

Liberton, M., Saha, R., Jacobs, J.M., Nguyen, A.Y., Gritsenko, M.A., Smith, R.D., Koppenaal, D.W. and Pakrasi, H.B. 2016 “Global Proteomic Analysis Reveals an Exclusive Role of Thylakoid Membranes in Bioenergetics of a Model Cyanobacterium” Molecular & Cellular Proteomics 15.6 | DOI 10.1074/mcp.M115.057240

Stingaciu, L.-R., O’Neill, H., Liberton, M., Urban, V.S., Pakrasi, H.B., and Ohl, M.  2016  “Revealing the Dynamics of Thylakoid Membranes in Living Cyanobacterial Cells” Scientific Reports 6:19627 | DOI 10.1038/srep19627