Clathrin lattice reorganization: theoretical considerations

We wish to postulate a mechanism by which flat hexagonal lattices of clathrin trimers transform into coated pits. Using an established model for packing trimers into lattices, we explored the assembly process by single addition of trimers to form polygons. Subject to favorable conditions, removal of a single trimer from a hexagon could lead to the formation of a pentagon. Elimination of trimers from polygonal sheets can occur either at the center of the network or at the edges. Removal of a trimer from the center of these adjacent polygons, “hub transformation,” is possible in very few instances, whereas removal from the edges of a polygonal sheet, “fringe transformation,” is possible in a host of cases. These hypothetical constructs can be used effectively to explain intermediate structures actually observed in flat hexagonal lattices. The geometry of a purely hexagonal lattice seems to dictate that the first step in transformation must be a “fringe transformation,” which then will allow subsequent “hub transformations” to take place leading to the introduction of pentagons into the center of the lattice and ultimately to the curvature of the clathrin lattice.