Structural atlas of the intact jumbo phage phiKZ

Jumbo phage phiKZ, a key model for studying phage nucleus formation and bacterial defense mechanisms, possesses a highly complex tail machine that is essential for infection. Here, we present the structural atlas of the intact jumbo phage phiKZ by cryo-EM, thereby identifying 40 constituent proteins and unveiling its modular architecture. The virion, with a length of approximately 360 nm, is comprised of an icosahedral capsid of 2520 polypeptide chains from 11 proteins, and a massive tail machine of over 900 polypeptide chains from 29 proteins. The tail features a unique, multi-layered neck and a highly elaborate baseplate. The neck is reinforced by whisker-like proteins and anchors the contractile tail, which terminates in the baseplate. The baseplate is constituted by a central hub, an inner periphery of interlocking wedge heterotrimers and hexagonal rings, and an outer periphery with a striking hexagonal star configuration. This intricate peripheral region of the baseplate serves as an extended platform for twelve peripheral fibers, which mediate host cell adsorption. Our findings provide a structural framework for understanding jumbo phage assembly and infection, thus contributing to the foundation for future functional studies and rational engineering of these phages for potential therapeutic applications. Jumbo phages are bacterial viruses with large genomes, oversized icosahedral capsids and complex tail architectures. Here, the authors use cryo-EM to provide a detailed structural analysis of jumbo phage phiKZ.