Localization of the inner body in jumbo phage phiK601 by Cryo-EM and high-dose imaging

Abstract

Jumbo bacteriophages possess exceptionally large capsids accommodating genomes that encode additional proteins, which support their infection and replication. A distinctive structural element, known as the inner body, has been observed in a number of phiKZ-like phage particles and its proteins are believed to play an essential role in phage genome organization and ejection. However, the precise localization and three-dimensional structure of the inner body have remained elusive. Here, we applied the high-dose cryo-electron microscopy (“bubblegram”) approach to localize the inner body within the capsid of phiKZ-like jumbo phage phiK601. The inner body was resolved as a cylindrical structure approximately 22 nm in diameter, tilted by ~ 20° relative to the tail axis and positioned asymmetrically, likely contacting the portal vertex and the opposing capsid edge. It is surrounded by 17 concentric layers of packaged DNA and exhibits positional flexibility within the capsid.

Keywords

jumbo phage / cryo-electron microscopy / inner body / bubblegrams / phiK601

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