CryoEM structure of the outer membrane secretin channel pIV from the f1 filamentous bacteriophage

Abstract

The Ff family of filamentous bacteriophages infect gram-negative bacteria, but do not cause lysis of their host cell. Instead, new virions are extruded via the phage-encoded pIV protein, which has homology with bacterial secretins. Here, we determine the structure of pIV from the f1 filamentous bacteriophage at 2.7 Å resolution by cryo-electron microscopy, the first near-atomic structure of a phage secretin. Fifteen f1 pIV subunits assemble to form a gated channel in the bacterial outer membrane, with associated soluble domains projecting into the periplasm. We model channel opening and propose a mechanism for phage egress. By single-cell microfluidics experiments, we demonstrate the potential for secretins such as pIV to be used as adjuvants to increase the uptake and efficacy of antibiotics in bacteria. Finally, we compare the f1 pIV structure to its homologues to reveal similarities and differences between phage and bacterial secretins.

A Novel and Ubiquitous Marine Methylophage Provides Insights into Viral-Host Coevolution and Possible Host-Range Expansion in Streamlined Marine Heterotrophic Bacteria

“…S10A). In this conformation, CsgGF is structurally similar to a secretin, a large protein superfamily used for macromolecule transport across the outer membrane such as DNA for natural competence (e.g., PilQ within the type IV secretion system in Vibrio cholerae ) or extrusion of filamentous phages during chronic infection (e.g., pIV in bacteriophages Ff) ( 84 ). Like CsgGF in an inverted conformation, PilQ comprises a β-barrel, with a secondary pore below, attached by two hinged α-helices.…”

The M13 Phage Assembly Machine Has a Membrane-Spanning Oligomeric Ring Structure

“…The particles also showed white dots, which might have indicated protrusions, possibly the ATPase domains of G1p that are located in the cytoplasm [3]. The outer diameter of the particles was determined to be about 12 nm, which fit with the dimensions of its counterpart in the outer membrane, the G4p secretin [7]. The secretin has an outer diameter of 11 nm and is composed of fifteen subunits, each spanning the outer membrane and with 4 β-strands resulting in a porin-like structure containing 60 β-strands.…”

“…The secretion of the progeny particle starts when multiple copies of the membrane-inserted major coat protein, G8p, are laterally fed into the M13 assembly machine [1,6]. All 2750 copies of G8p coat the DNA strand in a shingle-like helical arrangement and the growing particle leaves the inner membrane and moves across the outer membrane by extrusion through the inner cavity of the G4p secretin [7,8]. At the end of the secretion process the complex binds the transmembrane G3p and G6p to complete the formation of the particle.…”

A White Plaque, Associated with Genomic Deletion, Derived from M13KE-Based Peptide Library Is Enriched in a Target-Unrelated Manner during Phage Display Biopanning Due to Propagation Advantage

“…A lower copy number of pVIII might help the phage propagate faster. Electron microscopy (EM) techniques have already been used to characterize filamentous phages such as M13, providing detailed structural information with respect to the geometry and morphology of these phages as well as the structures of their different proteins [ 27 , 28 , 29 , 30 , 31 , 32 , 33 ]. Based on this, the use of EM holds potential to obtain insights into the length and structure of white-Ph-WSLGYTG.…”