Phage Pierces the Host Cell Membrane with the Iron-Loaded Spike

Abstract

Bacteriophages with contractile tails and the bacterial type VI secretion system have been proposed to use a special protein to create an opening in the host cell membrane during infection. These proteins have a modular architecture but invariably contain an oligonucleotide/oligosaccharide-binding (OB-fold) domain and a long β-helical C-terminal domain, which initiates the contact with the host cell membrane. Using X-ray crystallography and electron microscopy, we report the atomic structure of the membrane-piercing proteins from bacteriophages P2 and ϕ92 and identify the residues that constitute the membrane-attacking apex. Both proteins form compact spikes with a ∼10Å diameter tip that is stabilized by a centrally positioned iron ion bound by six histidine residues. The accumulated data strongly suggest that, in the process of membrane penetration, the spikes are translocated through the lipid bilayer without undergoing major unfolding.

Cryo‐ EM reconstruction of Type VI secretion system baseplate and sheath distal end

“…Overall dimensions of the baseplate are 182 Å in the narrow part, 240 Å in the broad part below the sheath–tube, and 195 Å in height including the protruding tip complex (Fig 2A and B). The central tip protrudes ~40 Å below base of the cone and clearly resembles a central spike present in all baseplates of phages with contractile tails (Browning et al , 2012; Leiman & Shneider, 2012; Schwarzer et al , 2012; Harada et al , 2013; Shneider et al , 2013; Habann et al , 2014; Taylor et al , 2016). …”

“…The signal to trigger sheath contraction is currently unknown for T6SS; however, in phages, the conformational switch of the baseplate triggers contraction of the assembled sheath, which then pushes the rigid tube with the sharp tip through the target cell membranes attached by tail fibers (Browning et al , 2012; Leiman & Shneider, 2012; Hu et al , 2015; Taylor et al , 2016). The signal for the phage baseplate component rearrangement comes from the attachment of the tail fibers to a target cell (Hu et al , 2015).…”

Structural investigations of a Podoviridae streptococcus phage C1, implications for the mechanism of viral entry

“…However, a possible tail spike protein, gp29 of Siphoviridae phage ISP (SPO1-like phage), is also predicted to have a TIM barrel domain by HHpred. Although the probability score for the C1 ORF13 structural prediction is not high, such a score was sufficient to predict domain structures for other proteins (21,(23)(24)(25). It had been previously suggested that ORF6 could be an appendage, based on sequence comparison (7).…”

Bacteriophage P2

“…53 The product of gene V makes up the small spike at the tip of the tail; it is a trimeric iron-binding protein involved in membrane penetration. [54][55][56][57] The W gene product is homologous to the T4 phage gp25, which is part of the T4 baseplate; it has been localized to the top of the baseplate, 47 and copurifies with gpV. 57 The J gene product lies at the edge of the baseplate; 57 gpJ and gpI are believed to make up the baseplate wedges.…”