Structural polymorphism of two-dimensional lattices assembled from baculoviral capsid proteins

Protein nanotubes (PNTs) can be regarded as two-dimensional (2D) lattices with p1 or p2 symmetry rolled into tubes. However, attempts to re-assemble their building blocks into stable 2D nanomaterials often fail. Here, starting from two baculoviral capsid proteins, we screened protein variants for the in vitro assembly of various nanotubes and nanosheets. These high-order assemblies were structurally characterized by cryo-electron microscopy techniques. Interfacial analysis of three groups of PNTs revealed that helical heterogeneity is largely the result of the redundancy of p2 symmetry-related contacting interfaces. The assembled nanosheets showed similar interfacial networks to their nanotubular counterparts. In addition, foreign macromolecules could be efficiently displayed on the size-controllable double-layered nanosheets. This study sheds light on the rational design of flexible nanosheets, and it also provides novel 2D protein scaffolds for developing biocompatible materials.