Large self-assembled clathrin lattices spontaneously disassemble without sufficient adaptor proteins
Fig 5
Clathrin lattices start as monomers that face an initial barrier to growth, with a stable size reached only after significant growth.
(A) The probability of observing clathrin lattices of size n can be converted to an energy-like metric −ln (P(n)), which at equilibrium is a true free energy in units of kBT. An initial barrier (in n) to nucleation plateaus, followed by a relatively flat region, where structures have comparable probability. Across the full time-dependent trajectory shown in the upper inset, we analyze lattices sampled across the full trajectory (green dots), the growth phase (yellow dots), and equilibrium (orange dots). During growth, clathrin forms intermediate size lattices, while at equilibrium, only small and large lattices are visible. [AP2] = 1.6μM. (B) To quantify the end of the initial barrier to growth (n1), and the start to the stabilized growth (n2), we define a plateau at constant −ln (P(n)) that defines these intercepts for each trajectory (Text A in S1 Text). (C) With increasing adaptor concentration, larger lattices become stabilized. The shape of the curves are consistent with the data in Fig 4A; the free energy forms a trough at higher concentrations, consistent with the average size of lattices at equilibrium. (D) The critical size where the barrier plateaus is ~n1 = 25, independent of adaptor concentration. The noisy plateau region is followed by a well that starts at n2 and increases with increasing adaptor concentration. (Inset) With higher adaptor concentration, the time to cross the first barrier at n1 is faster, following the inverse of adaptors τobs∝1/[AP2], with a proportionality constant 1/[0.026μM-1s-1].