Protein cages such as virus-like particles (VLPs), ferritins, and encapsulins assemble from a distinct number of protein subunits into hollow spherical structures. They have advantageous properties, including high stability, size homogeneity, and the ability to sequester guest cargo. These characteristics make them an attractive platform to develop new nanomaterials. Gold Nanoparticles (AuNPs) in particular, are of considerable interest in protein cage encapsulation due to their optoelectronic properties. This research focuses on the encapsulation of AuNPs inside of VLPs derived from a bacteriophage, P22. P22 VLPs are ideal for this study due to the generous size of their inner cavity, roughly 50 nm, and their scaffolding protein (SP) mediated assembly mechanism. P22 has been established as a viable model for the study of cage assembly. Roughly 100-300 SP serve as an essential template for cage construction by interacting with the 420 coat protein (CP) subunits required to form a VLP, 56 nm in diameter. Interestingly, P22 SP can be genetically modified while maintaining the ability to facilitate morphologically consistent cage assembly in vitro. In this study we have genetically engineered two viable SP constructs with a peptide motif (CGGSENT) which exhibits high binding affinity for gold. We confirmed that the SP mutants mediate assembly of CPs into VLPs comparative to the wild-type P22 SP (Fig 1). Next, we introduce the SP mutants on the surface of AuNPs through a ligand exchange reaction. It is anticipated that the SP-decorated AuNPs will initiate the assembly of CP into a capsid structure around the AuNPs.

<b>Figure 1:</b> TEM images of P22 VLP cages assembled <i>in vitro</i> using WTCP with WTSP (A) and WTCP with AuBP-SP (B) show that assembly using the genetically modified SP results in homogenous cages similar in size and morphology to those assembled using the wild-type SP.

Figure 1: TEM images of P22 VLP cages assembled in vitro using WTCP with WTSP (A) and WTCP with AuBP-SP (B) show that assembly using the genetically modified SP results in homogenous cages similar in size and morphology to those assembled using the wild-type SP.

Randy Espinoza

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