Modular Protein–DNA Cocrystals as Precise, Programmable Assembly Scaffolds

High-precision nanomaterials to entrap DNA-binding molecules are sought after for applications such as controlled drug delivery and scaffold-assisted structural biology. Here, we engineered protein–DNA cocrystals to serve as scaffolds for DNA-binding molecules. The designed cocrystals, isoreticular cocrystals, contain DNA-binding protein and cognate DNA blocks where the DNA–DNA junctions stack end-to-end. Furthermore, the crystal symmetry allows topology preserving (isoreticular) expansion of the DNA stack without breaking protein–protein contacts, hence providing larger solvent channels for guest diffusion. Experimentally, the resulting designed isoreticular cocrystal adopted an interpenetrating I222 lattice, a phenomenon previously observed in metal–organic frameworks (MOFs). The interpenetrating lattice crystallized dependably in the same space group despite myriad modifications at the DNA–DNA junctions. Assembly was modular with respect to the DNA inserted for expansion, providing an interchangeable DNA sequence for guest-specified scaffolding. Also, the DNA–DNA junctions were tunable, accommodating varied sticky base overhang lengths and terminal phosphorylation. As a proof of concept, we used the interpenetrating scaffold crystals to separately entrap three distinct guest molecules during crystallization. Isoreticular cocrystal design offers a route to a programmable scaffold for DNA-binding molecules, and the design principles may be applied to existing cocrystals to develop scaffolding materials