A 2-dimensional ratchet model describes assembly initiation of a specialized bacterial cell surface

Significance The assembly of localized static structures is a culminating feature of developmental programs. Construction of the spore coat, a shell that surrounds bacterial spores, is a model for understanding how proteins localize and assemble at the correct place and time during morphogenesis. Using data derived from in vivo and in vitro single-molecule imaging, we propose a computational model in which coat assembly initiates via an interplay between 2 proteins: a protein that localizes preferentially to micron-scale convex membranes (the surface of the developing spore) and a recruited structural protein that polymerizes to hold the first protein in place. This ratchet model therefore describes how a static structure can be built specifically atop the 2-dimensional surface of a developing organelle.