Viral scaffolds are protein-based biopolymers and can be tuned for applications' through chemical surface modulation or genetic display. Among these, bacteriophage T4, which contains an icosahedral head encapsulating DNA and a tail, has attracted our attention due to its accessibility and properties. Tailless T4 heads can be produced in E. coli and genetically manipulated in the laboratory. The head is a nano size particle, 90 nm in width and 100nm in length, and is among the largest one in dsDNA pages. T4 nanoparticles (NP) cover large head surface areas which accommodate many more functional groups besides icosahedral phages. This gives them more flexibility for surface functionalization than most other icosahedral viruses. In addition, the heads can genetically display dual peptides/proteins through their flexible display system. This program conducts studies to understand the chemical properties of engineered tailless T4 NP and explore the applications of the resulting T4NP.

(a) Atomic Force Microscopy (AFM) image showing the coverage and ordering of mutant bacteriophage T4 on a mica substrate. (b) Corresponding 3D surface plot.
(a) Atomic Force Microscopy (AFM) image showing the coverage and ordering of mutant bacteriophage T4 on a mica substrate. (b) Corresponding 3D surface plot.

T4NP as detection elements and biomaterials: Since multiple copies of antibodies can be displayed on teh same head surface, antibodies displayed T4NP may exhibit hight binding affinity due to the increase of avidity. Taking advantage of flexible fispaly system, tailless T4 NPs displaying anti-toxin antibodies are eingineered genetically and characterized for toxin binding interaction and specificity. Using a newly established protocol, dispersed tailless T4 NPs and displayed T4 NPs are purified and can assemble into a monolayer on the solid substrates as well. The dispersed T4NPs are also used as a template for chemical modification or dye conjugation.

 

Dyes are cross-linked to tailless T4 NPs through amine groups and the resulting highly fluorescent dye-T4 can enter eukaryotic cells as shown in the right confocal image.
Dyes are cross-linked to tailless T4 NPs through amine groups and the resulting highly fluorescent dye-T4 can enter eukaryotic cells as shown in the right confocal image.

Dye modified T4NP as intracellular imaging probes: T4 NPs are stable enough to endure the chemical reactions in the presence of some organic solvents, such as DMSO and Chloroform. Dye can be cross linked onto T4 NPs through surface functional groups, such as reactive amine and carboxyl. The resulting dye-T4 NPs are also stable and intact. They are used as the intracellular probes for flow cytometry and optical imaging. This is the first time to demonstrate that icosahedra bacteriophage heads can get into the cells and serve as intracellular probes.