Skip to main content
. 2019 Oct 9;116(43):21789–21799. doi: 10.1073/pnas.1907397116

Fig. 7.

Fig. 7.

A quantitative model for coat assembly initiation incorporating dynamic, but preferential, localization of SpoVM coupled to localized polymerization of recruited SpoIVA. (A and B) Schematic of the spherical forespore surface (A) modeled as a 2-dimensional lattice containing 3 coat assembly intermediates (B): 1) bound SpoVM (blue), 2) SpoIVA (magenta) recruited to bound SpoVM, and 3) polymerized SpoIVA atop membrane-bound SpoVM. (k1 and k−1) and (k2 and k−2): association and dissociation rates of SpoVM on and from the membrane or SpoIVA on and from membrane-bound SpoVM, respectively. (k3): polymerization rate of 3 or more adjacently recruited SpoIVA molecules. (C) Range of values for k3 determined by running multiple simulations with experimentally determined (k1 and k−1) and (k2 and k−2) that resulted in 50% SpoIVA polymerization between 2 to 3 h. (D) Simulation, using cellular concentrations of SpoVM and SpoIVA, that tracks abundance of assembly intermediates over time. First graph: first millisecond of the reaction, SpoVM binds to membrane (blue) and recruits SpoIVA to produce membranes bound to both SpoVM and SpoIVA (magenta). Black: free SpoVM; green: membranes harboring polymerized SpoIVA atop SpoVM. Second and third graphs: first 10 milliseconds and 1,000 s of the simulation. Polymerized SpoIVA atop membranes shown in green. Fourth graph: first 10,000 s of the simulation. Polymerization of SpoIVA drives depletion of membranes simply bound by SpoVM and SpoIVA (magenta). (E) Fluorescence microscopy of SpoVM-Cy3 (0.3 or 0.9 µM) binding to a mixed population of 2 and 8 µm SSLBs either in the presence (Left) or absence (Right) of SpoIVA and ATP. (E) Cy3 fluorescence (top row); merge, Cy3 and DIC (bottom row). (Scale bar: 4 μm.) (F) Quantification of SpoVM-Cy3 fluorescence bound to 2-µm (maroon) or 8-µm (blue) SSLBs. P values: *** < 0.005; otherwise, >0.05.