A Ph-Responsive Virus-Like Particle (VLP) as A Protein Cage for A Targeted Delivery.

A stimuli-responsive protein self-assembly offers promising utility as a protein nanocage for biotechnological and medical applications. Herein, we report the development of a virus-like particle (VLP) that undergoes a transition between assembly and disassembly under a neutral and acidic pH, respectively, for a targeted delivery. The structure of bacteriophage P22 coat protein was used for the computational design of coat subunits that self-assemble into a pH-responsive VLP. Subunit designs were generated through iterative computational cycles of histidine substitutions and evaluation of the interaction energies among the subunits under an acidic and neutral pH. We tested the top subunit designs and selected one that assembled into a VLP showing the highest pH-dependent structural transition. The cryo-EM structure of the VLP was determined, and the structural basis of a pH-triggered disassembly was delineated. The utility of the designed VLP was exemplified through a targeted delivery of a cytotoxic protein cargo into tumor cells in a pH-dependent manner. Our results provide strategies for the development of self-assembling protein architectures with a new functionality for diverse applications. This article is protected by copyright. All rights reserved.