S-layer protein. The S-layer is a paracrystalline mono-layered assembly of proteins which coats the surface of bacteria (PubMed:24078613). Under laboratory conditions, has a supportive but not a critical role in the function of the cyanobacterium (PubMed:24078613). Shows no apparent hemolytic activity against sheep erythrocytes, however, a slight hemolytic activity is detected during the conformational change caused by the rebinding of Ca(2+) (PubMed:16672608). Contains GGXGXDXUX nonapeptide motifs, which are found in members of the repeat in toxin (RTX) protein family, and which are implicated in Ca(2+) binding. Binds Ca(2+) and shows Ca(2+)-induced reversible conformational changes. Glycosylated. The deletion mutant has similar pigmentation, but a more flat, spread morphology and a shiny surface. It displays a smooth lipopolysaccharide surface as its most peripheral layer. Viability of the mutant is reduced upon exposure to lysozyme treatment and hypo-osmotic stress.