Fig. 1.

The BMC structural proteins forming a polyhedral shell. a The four different types of building blocks: BMC-P (pentamer monomer in yellow); BMC-H hexamer (monomer in blue); BMC-T^S trimer (monomer in green), and the double stacked BMC-T^D hexamer (monomer in each layer in green). A top view and a side view are shown, as well as a close up of the center for the BMC-P, BMC-H, and BMC-T^S. The BMC-T^D pore can have an open or closed conformation (closed conformation is shown). The shell proteins have a concave and a convex side, the concave side faces outward (towards the top of the side view), while the convex side faces the BMC lumen (towards the bottom of the side view). b The structure of a BMC shell from Haliangium ochraceum and a schematic of the icosahedral symmetry (BMC-H in blue; BMC-T^S and BMC-T^D in green; BMC-P in yellow)