Complex polyhedron assembled from proteins

Biochemists have coaxed a protein to assemble into a snub-cube-shaped cage. Snub cubes, which have 38 faces—6 squares and 32 equilateral triangles—are one of the 13 Archimedean solids, first described more than 2,000 years ago by the Greek mathematician Archimedes. These structures possess convex shapes, identical vertices, and faces that are regular polygons. Until now, no one had built a snub-cube-like structure from biological molecules. A team led by Jonathan G. Heddle of Poland’s Jagiellonian University created the structure using the trp RNA-binding attenuation protein (TRAP). TRAP consists of 11 protein subunits that come together in a structure called an undecamer. To make it possible to build larger structures from the TRAP undecamers, the team swapped lysine residues at TRAP’s perimeter for cysteines. Gold(I) or mercury(II) brings some of the cysteines’ thiols together, pulling 24 of the undecamers into a snub-cube-like cage (Nature 2019, DOI: 10.1038/s41586-019-1185-4). The cages can withstand temperatures of 95 °C and extremes of pH, but adding a little reducing agent, such as dithiothreitol, prompts them to disassemble. This stability and controllable disassembly “hints at potential applications as an intracellular delivery agent,” the researchers write. They also say this study establishes an approach for linking protein components into previously unexplored geometries.