Double-Helix Duality: Rods Bow, Toroids Wow in the Nuclease Arena.

Utilizing polyion complexation, the formation of rod-like DNA condensates is driven by the intrinsic rigidity of supramolecular plasmid DNA. Upon interaction with polycationic block copolymers of poly(ethylene glycol)-polylysine (PEG-PLys), these macromolecules undergo a regular self-folding process, during which double-stranded DNA (dsDNA) transitions into single-stranded DNA (ssDNA) at the kinked junctions. Our investigations, employing transmission electron microscopy (TEM), unprecedentedly reveal the absence of a PEG coating at these critical junctions, rendering them susceptible to nuclease degradation. This finding underscores the critical necessity for comprehensive PEG encapsulation in the engineering of robust gene delivery constructs. In stark contrast to the anisotropic rod-like condensates, our novel isotropic toroidal DNA condensates, characterized by comprehensive PEG shielding and a self-spooling mechanism that preserves dsDNA integrity, exhibit a marked enhancement in enzymatic stability (nearly 30-fold greater). Their favorable condensation process also confers superior transcriptional potential, positioning these toroidal condensates as promising platforms for the next generation of gene delivery systems.