T5 elaborates its icosahedral capsid independently from its tail. The capsid is initially assembled into a Prohead I the from 775 copies of the head protein pb8, which includes an N-terminal scaffolding domain, the dodecameric portal protein pb7 that forms a gate located at a unique vertex, and the protease pb11. The proteolytic maturation of all the capsid protein subunits by pb11 converts this Prohead I into Prohead II. Packaging of the DNA into Prohead II through the portal pore is driven by a molecular motor called terminase and results in the expansion of the capsid shell, allowing for accommodation of the full-length genome. Finally, the filled capsid is closed by the oligomeric head completion protein p144, forming the attachment site for T5 tail. The mature capsid is decorated with pb10, a monomeric protein that anchors to the capsid outer surface with an extremely high affinity. Pb10 is located at the center of the 120 hexamers of pb8, which form the 20 faces of the icosahedral capsid shell.
Current work in the lab investigates the proteolytic mechanisms that maturate Prohead I into Prohead II and plans to exploit the remarkable properties of the two-domain decoration protein pb10. These studies open new avenues for the production of phage-inspired versatile nanocarriers for biotechnological or medical applications