Stabilizing DNA–Protein Co-Crystals via Intra-Crystal Chemical Ligation of the DNA

Porous protein crystals: synthesis and applications

Large-pore protein crystals (LPCs) are an emerging class of biomaterials. The inherent diversity of proteins translates to a diversity of crystal lattice structures, many of which display large pores and solvent channels. These pores can, in turn, be functionalized via directed evolution and rational redesign based on the known crystal structures. LPCs possess extremely high solvent content, as well as extremely high surface area to volume ratios. Because of these characteristics, LPCs continue to be explored in diverse applications including catalysis, targeted therapeutic delivery, templating of nanostructures, structural biology. This Feature review article will describe several of the existing platforms in detail, with particular focus on LPC synthesis approaches and reported applications.

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.

Conditionally designed luminescent DNA crystals doped by Ln3+(Eu3+/Tb3+) complexes or fluorescent proteins with smart drug sensing property

In this work, a designed porous DNA crystal with high intrinsic biocompatibility was used as the scaffold material to load fluorescent guest molecules to detect anti-cancer drugs. It is shown here that the synthesized crystals have the characteristics consistent with the designed large solvent channels, and can therefore accommodate guest molecules such as fluorescent proteins that cannot be accommodated by less porous crystals. Eu(TTA)₃phen and Tb(acac)₃phen lanthanide complexes were individually noncovalently loaded into the porous crystals, resulting in hybrid luminescent DNA crystals. Emodin, an anti-cancer, anti-tumor, anti-inflammatory drug, was found to quench lanthanide complexes in solution or in crystals. Notably, emodin is the active ingredient of Lianhua Qingwen Capsule, an anti-COVID-19 drug candidate. Therefore, the porous DNA crystals reported here have potential applications as a biocompatible and theranostic delivery biomaterial for functional macromolecules.