(A) Structural elements for Flo11-directed discrimination. Shown are ScFlo11A, ScΣFlo11A and KpFlo11A variants that differ either by the topology of the conserved aromatic bands shown as orange or green rings, respectively, or by an additional insertion shown in magenta. The Flo11BC domain is shown as beige spheres. (B) Model for bi-molecular Flo11A-Flo11A trans-interaction. Cell surfaces are shown in yellow and trans-interaction is indicated as grey, dotted arrow. (C) Model for interaction of Flo11A collectives by cis- and trans-interactions. Collective-forming cis-interactions are indicated as white, dotted arrows.