"Gated Junctions" in vielzelligen Cyanobakterien
Zellbiologie
Zusammenfassung der Projektergebnisse
Cell-to-cell communication is a prerequisite for the functioning of a multicellular organism. The most highly organized multicellular bacteria are found in the phylum cyanobacteria, where filaments may consist of hundreds of tightly interconnected cells. In the filamentous cyanobacterium Anabaena (Nostoc) sp. PCC 7120, heterocysts differentiate from vegetative cells in a semi-regular pattern and are specialized in nitrogen fixation. Both cell types fulfill specific metabolic tasks and are interconnected in a homeostatic network of the entire multicellular filament. Transport of molecules and cell-cell communication along the filament occurs through the septal cell wall by multimeric protein structures, the septal junctions. In previous studies we have identified a nanopore array in the septal peptidoglycan and solved the in situ architecture of septal junctions by cryo electron tomography (CET). The septal junctions consist of a tube traversing the septal peptidoglycan inside the nanopores, comprise a plug inside the cytoplasmic membrane, which contains the FraD protein. The plug is covered by a cap structure with 5-fold symmetry on the cytosolic side. Fluorescence recovery after photobleaching showed that cell-cell communication was blocked upon stress in a reversible manner. This gating was accompanied by a reversible conformational change in the cap. By co immune precipitation with the septal junction component FraD, we here identified a list of putative septal junction proteins and analyzed them by mutant characterization. We found a putative plug forming protein, SepN, which probably connects to the cap structure and the membrane by the FraD protein, as shown by high resolution CET. Another identified protein, is the septal protein FraI, which is absolutely required for nanopore formation and building the septal junctions thru the septum. We also investigated the function of the homolog FraI protein in Nostoc punctiforme and showed that the nanopore array is required for proper cell differentiation and function of differentiated cells, like heterocysts and hormogonia. We finally obtained interesting insights in the biological function of the gating mechanism by performing survival studies after UV treatment. Mutants in FraD and SepN, which cannot close their septal junctions upon stress, do not survive the treatment demonstrating that gating is an important factor of survival of the filaments upon stress. In this work, the complex network of proteins involved in cell-cell communication and the understanding of regulation of intercellular exchange were greatly extended and the architecture of the septal junctions with suggested participation of distinct proteins presented by high resolution.
Projektbezogene Publikationen (Auswahl)
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Cell–cell communication through septal junctions in filamentous cyanobacteria. Current Opinion in Microbiology, 61, 35-41.
Kieninger, Ann-Katrin & Maldener, Iris
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SepN is a septal junction component required for gated cell–cell communication in the filamentous cyanobacterium Nostoc. Nature Communications, 13(1).
Kieninger, Ann-Katrin; Tokarz, Piotr; Janović, Ana; Pilhofer, Martin; Weiss, Gregor L. & Maldener, Iris
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The role of FraI in cell–cell communication and differentiation in the hormogonia-forming cyanobacterium Nostoc punctiforme. mSphere, 9(8).
Janović, Ana; Maldener, Iris; Menzel, Claudia; Parrett, Gabriel A. & Risser, Douglas D.
