Structure-based design of ferritin nanoparticle immunogens displaying antigenic loops of .

Effective vaccines are urgently needed to combat gonorrhea, a common sexually transmitted bacterial infection, for which treatment options are diminishing due to rapid emergence of antibiotic resistance. We have used a rational approach to the development of gonorrhea vaccines, and genetically engineered nanoparticles to present antigenic peptides of , the causative agent of gonorrhea. We hypothesized that the ferritin nanocage could be used as a platform to display an ordered array of antigenic peptides on its surface. MtrE, the outer membrane channel of the highly conserved gonococcal MtrCDE active efflux pump, is an attractive vaccine target due to its importance in protecting from host innate effectors and antibiotic resistance. Using computational approaches, we designed constructs that expressed chimeric proteins of the ferritin and antigenic peptides that correspond to the two surface-exposed loops of MtrE. The peptides were inserted at the N terminus or in a surface-exposed ferritin loop between helices αA and αB. Crystal structures of the chimeric proteins revealed that the proteins assembled correctly into a 24-mer nanocage structure. Although the inserted peptides were disordered, it was clear that they were displayed on the nanocage surface, but with multiple conformations. Our results confirmed that the ferritin nanoparticle is a robust platform to present antigenic peptides and therefore an ideal system for rational design of immunogens.