PT  - JOURNAL ARTICLE
AU  - Benjamin L. Springstein
AU  - Dennis J. Nürnberg
AU  - Christian Woehle
AU  - Julia Weissenbach
AU  - Marius L. Theune
AU  - Andreas O. Helbig
AU  - Iris Maldener
AU  - Tal Dagan
AU  - Karina Stucken
TI  - Two novel heteropolymer-forming proteins maintain multicellular shape of the cyanobacterium <em>Anabaena</em> sp. PCC 7120
AID  - 10.1101/553073
DP  - 2020 Jan 01
TA  - bioRxiv
PG  - 553073
4099  - http://biorxiv.org/content/early/2020/06/05/553073.short
4100  - http://biorxiv.org/content/early/2020/06/05/553073.full
AB  - Polymerizing and filament-forming proteins are instrumental for numerous cellular processes such as cell division and growth. Their function in stabilization and localization of protein complexes and replicons is achieved by a filamentous structure. Known filamentous proteins assemble into homopolymers consisting of single subunits – e.g. MreB and FtsZ in bacteria – or heteropolymers that are composed of two subunits, e.g. keratin and α/β tubulin in eukaryotes. Here, we describe two novel coiled-coil-rich proteins (CCRPs) in the filament forming cyanobacterium Anabaena sp. PCC 7120 (hereafter Anabaena) that assemble into a heteropolymer and function in the maintenance of the Anabaena multicellular shape (termed trichome). The two CCRPs – Alr4504 and Alr4505 (named ZicK and ZacK) – are strictly interdependent for the assembly of protein filaments in vivo and polymerize nucleotide-independently in vitro, similar to known intermediate filament (IF) proteins. A ΔzicKΔzacK double mutant is characterized by a zigzagged cell arrangement and hence a loss of the typical linear Anabaena trichome shape. ZicK and ZacK interact with themselves, with each other, with the elongasome protein MreB, the septal junction protein SepJ and the divisome associate septal protein SepI. Our results suggest that ZicK and ZacK function in cooperation with SepJ and MreB to stabilize the Anabaena trichome and are likely essential for the manifestation of the multicellular shape in Anabaena. Our study reveals the presence of filament-forming IF-like proteins whose function is achieved through the formation of heteropolymers in cyanobacteria.Competing Interest StatementThe authors have declared no competing interest.