The architecture and stabilisation of flagellotropic tailed bacteriophages

Abstract

Flagellotropic bacteriophages engage flagella to reach the bacterial surface as an effective means to increase the capture radius for predation. Structural details of these viruses are of great interest given the substantial drag forces and torques they face when moving down the spinning flagellum. We show that the main capsid and auxiliary proteins form two nested chainmails that ensure the integrity of the bacteriophage head. Core stabilising structures are conserved in herpesviruses suggesting their ancestral origin. The structure of the tail also reveals a robust yet pliable assembly. Hexameric rings of the tail-tube protein are braced by the N-terminus and a β-hairpin loop, and interconnected along the tail by the splayed β-hairpins. By contrast, we show that the β-hairpin has an inhibitory role in the tail-tube precursor, preventing uncontrolled self-assembly. Dyads of acidic residues inside the tail-tube present regularly-spaced motifs well suited to DNA translocation into bacteria through the tail.

Architecture of the flexible tail tube of bacteriophage SPP1

“…S7 )—all featuring hexameric, helically stacked rings with subunits consisting of a β-sandwich-type fold and one parallel α-helix. Loop 40–59 is present at the interface between subunits in all described Siphoviridae phages 7 , 8 , 10 , 11 , Siphoviridae -like systems 12 and T4 phage 4 , suggesting that it is a conserved structural element across both Siphoviridae and Myoviridae families as it was also proposed to play a regulatory role during tail polymerization. The mentioned C-arm is only present in SPP1 and 80α 10 (even if not completely resolved).…”

“…It might be a critical element regulating the tail structure in a subgroup of Siphoviridae . YSD1 phage features a similar intermolecular contact—an inserted domain after the α-helix that similar to the C-arm folds onto the outer β-sheet of the β-sandwich of a neighboring subunit 11 . However, this contact is established within the ring and not between the rings.…”

“…However, this contact is established within the ring and not between the rings. Phages λ 8 and YSD1 11 carry an additional N-terminal loop that promotes intermolecular contacts. The organization of the tail tube of T5 phage is different since it uncommonly exhibits a trimeric ring resulting from the fusion of every two subunits within the hexamerization domain 7 .…”

“…In 2020, a cryo-EM model of the baseplate of the Staphylococcus aureus 80α phage was reported, which includes two rings of the tail tube that are anchored within the baseplate and are, thus, not part of the flexible tube region 10 . Also, cryo-EM models of the tails of the flagellotropic tailed bacteriophage YSD1 11 and the Siphoviridae -like gene transfer agent of Rhodobacter capsulatus 12 were reported recently. All models show a striking structural homology between TTPs from Myoviridae and Siphoviridae ; as well as between these phage TTPs and the tube-forming proteins from other injection systems, like the bacterial type VI secretion system 13 and the extracellular injection system from bacteria and archeae 14 .…”

The component parts of bacteriophage virions accurately defined by a machine-learning approach built on evolutionary features

“…Careful consideration is needed in selecting the phages for use in therapeutic cocktails (4–6), considerations made difficult because annotation of phage genomes is poor (7, 8), potentially obscuring phages with therapeutic potential. For example, while structural motifs are now known (9) that will promote phage virion stability (i.e. shelf-life), only with correct annotation of the major capsid, minor capsid and other proteins involved can structural motifs be identified and evaluated.…”