title: The Peptidoglycan-Binding Protein SjcF1 Influences Septal Junction Function and Channel Formation in the Filamentous Cyanobacterium Anabaena.
abstract: Filamentous, heterocyst-forming cyanobacteria exchange nutrients and regulators between cells for diazotrophic growth. Two alternative modes of exchange have been discussed involving transport either through the periplasm or through septal junctions linking adjacent cells. Septal junctions and channels in the septal peptidoglycan are likely filled with septal junction complexes. While possible proteinaceous factors involved in septal junction formation, SepJ (FraG), FraC, and FraD, have been identified, little is known about peptidoglycan channel formation and septal junction complex anchoring to the peptidoglycan. We describe a factor, SjcF1, involved in regulation of septal junction channel formation in the heterocyst-forming cyanobacterium Anabaena sp. strain PCC 7120. SjcF1 interacts with the peptidoglycan layer through two peptidoglycan-binding domains and is localized throughout the cell periphery but at higher levels in the intercellular septa. A strain with an insertion in sjcF1 was not affected in peptidoglycan synthesis but showed an altered morphology of the septal peptidoglycan channels, which were significantly wider in the mutant than in the wild type. The mutant was impaired in intercellular exchange of a fluorescent probe to a similar extent as a sepJ deletion mutant. SjcF1 additionally bears an SH3 domain for protein-protein interactions. SH3 binding domains were identified in SepJ and FraC, and evidence for interaction of SjcF1 with both SepJ and FraC was obtained. SjcF1 represents a novel protein involved in structuring the peptidoglycan layer, which links peptidoglycan channel formation to septal junction complex function in multicellular cyanobacteria. Nonetheless, based on its subcellular distribution, this might not be the only function of SjcF1.
  
  
  OBJECTIVE
  Cell-cell communication is central not only for eukaryotic but also for multicellular prokaryotic systems. Principles of intercellular communication are well established for eukaryotes, but the mechanisms and components involved in bacteria are just emerging. Filamentous heterocyst-forming cyanobacteria behave as multicellular organisms and represent an excellent model to study prokaryotic cell-cell communication. A path for intercellular metabolite exchange appears to involve transfer through molecular structures termed septal junctions. They are reminiscent of metazoan gap junctions that directly link adjacent cells. In cyanobacteria, such structures need to traverse the peptidoglycan layers in the intercellular septa of the filament. Here we describe a factor involved in the formation of channels across the septal peptidoglycan layers, thus contributing to the multicellular behavior of these organisms.
authors.affiliation: Institute for Molecular Biosciences, Goethe University, Frankfurt, Germany.
authors.forename: Mareike
authors.initials: M
authors.lastname: Rudolf
authors.affiliation: Institute for Molecular Biosciences, Goethe University, Frankfurt, Germany.
authors.forename: Nalan
authors.initials: N
authors.lastname: Tetik
authors.affiliation: Instituto de Bioquímica Vegetal y Fotosíntesis, CSIC and Universidad de Sevilla, Seville, Spain.
authors.forename: Félix
authors.initials: F
authors.lastname: Ramos-León
authors.forename: Nadine
authors.initials: N
authors.lastname: Flinner
authors.affiliation: Institute for Molecular Biosciences, Goethe University, Frankfurt, Germany.
authors.forename: Giang
authors.initials: G
authors.lastname: Ngo
authors.affiliation: Institute for Molecular Biosciences, Goethe University, Frankfurt, Germany.
authors.forename: Mara
authors.initials: M
authors.lastname: Stevanovic
authors.affiliation: Instituto de Bioquímica Vegetal y Fotosíntesis, CSIC and Universidad de Sevilla, Seville, Spain.
authors.forename: Mireia
authors.initials: M
authors.lastname: Burnat
authors.affiliation: Instituto de Bioquímica Vegetal y Fotosíntesis, CSIC and Universidad de Sevilla, Seville, Spain.
authors.forename: Rafael
authors.initials: R
authors.lastname: Pernil
authors.affiliation: Instituto de Bioquímica Vegetal y Fotosíntesis, CSIC and Universidad de Sevilla, Seville, Spain.
authors.forename: Enrique
authors.identifier: http://orcid.org/0000-0001-7605-7343
authors.initials: E
authors.lastname: Flores
authors.affiliation: schleiff@bio.uni-frankfurt.de.
authors.forename: Enrico
authors.initials: E
authors.lastname: Schleiff
mesh_terms: D017033:Anabaena / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D001422:Bacterial Adhesion; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D017353:Gene Deletion; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D016254:Mutagenesis, Insertional; D009586:Nitrogen Fixation; D010457:Peptidoglycan / Q000378:metabolism*; D011485:Protein Binding
chemical_list: D001426:Bacterial Proteins; D008565:Membrane Proteins; D010457:Peptidoglycan