Abstract
Filament-forming proteins in bacteria function in stabilization and localization of proteinaceous complexes and replicons; hence they are instrumental for myriad cellular processes such as cell division and growth. Here we present two novel filament-forming proteins in cyanobacteria. Surveying cyanobacterial genomes for coiled-coil-rich proteins (CCRPs) that are predicted as putative filament-forming proteins, we observed a higher proportion of CCRPs in filamentous cyanobacteria in comparison to unicellular cyanobacteria. Using our predictions, we identified nine protein families with putative intermediate filament (IF) properties. Polymerization assays revealed four proteins that formed polymers in vitro and three proteins that formed polymers in vivo. Fm7001 from Fischerella muscicola PCC 7414 polymerized in vitro and formed filaments in vivo in several organisms. Additionally, we identified a tetratricopeptide repeat protein - All4981 - in Anabaena sp. PCC 7120 that polymerized into filaments in vitro and in vivo. All4981 interacts with known cytoskeletal proteins and is indispensable for Anabaena viability. Although it did not form filaments in vitro, Syc2039 from Synechococcus elongatus PCC 7942 assembled into filaments in vivo and a Δsyc2039 mutant was characterized by an impaired cytokinesis. Our results expand the repertoire of known prokaryotic filament-forming CCRPs and demonstrate that cyanobacterial CCRPs are involved in cell morphology, motility, cytokinesis and colony integrity.
Highlights
Filament-forming proteins in bacteria function in stabilization and localization of proteinaceous complexes and replicons; they are instrumental for myriad cellular processes such as cell division and growth
Apart from Crescentin, many other coiled-coil-rich proteins (CCRPs) with intermediate filament (IF)-like functions have been identified to polymerize into filamentous structures and to perform cytoskeletal-like roles; none of them resembled the eukaryotic IF domain architecture (reviewed by Lin & Thanbichler (2013)19)
We search for CCRPs with presumed IF-like functions in cyanobacteria using a computational prediction of CCRPs
Summary
Filament-forming proteins in bacteria function in stabilization and localization of proteinaceous complexes and replicons; they are instrumental for myriad cellular processes such as cell division and growth. Together with FilP and a cellulose-synthase, these proteins form the polarisome, which guides peptidoglycan biogenesis and hyphal tip growth in S. coelicolor[30,32,33] Another example are four CCRPs in the human pathogen Helicobacter pylori, which were found to assemble into filaments in vitro and in vivo, with a function in determination of the helical cell shape as well as cell motility[34,35]. We search for CCRPs with presumed IF-like functions in cyanobacteria using a computational prediction of CCRPs. Putative filament-forming proteins were further investigated experimentally by structural analyses and in vitro and in vivo localization assays in morphologically diverse cyanobacteria
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