a-g, Plasticity of MCPs related to interactions with portal or CATC. Shown in (a) are the three types of vertices—CATC-absent penton vertex, CATC-binding penton vertex, and portal vertex—and how MCP subunits P1 and P6 are variably engaged in CATC or portal interactions. Corresponding MCPs were extracted from the three types of vertices and aligned. The superpositions of the three aligned P1 MCPs (b, with zoomed-in areas shown in c-e) and of the three aligned P6 MCPs f, with zoomed-in areas shown in g, show structural plasticity.