title: Structure of the filamentous phage pIV multimer by cryo-electron microscopy.
abstract: The homo-multimeric pIV protein constitutes a channel required for the assembly and export of filamentous phage across the outer membrane of Escherichia coli. We present a 22 A-resolution three-dimensional reconstruction of detergent-solubilized pIV by cryo-electron microscopy associated with image analysis. The structure reveals a barrel-like complex, 13.5 nm in diameter and 24 nm in length, with D14 point-group symmetry, consisting of a dimer of unit multimers. Side views of each unit multimer exhibit three cylindrical domains named the N-ring, the M-ring and the C-ring. Gold labeling of pIV engineered to contain a single cysteine residue near the N or C terminus unambiguously identified the N-terminal region as the N-ring, and the C-terminal region was inferred to make up the C-ring. A large pore, ranging in inner diameter from 6.0 nm to 8.8 nm, runs through the middle of the multimer, but a central domain, the pore gate, blocks it. Moreover, the pore diameter at the N-ring is smaller than the phage particle. We therefore propose that the pIV multimer undergoes a large conformational change during phage transport, with reorganization of the central domain to open the pore, and widening at the N-ring in order to accommodate the 6.5 nm diameter phage particle.
authors.affiliation: The Rockefeller University, 1230 York Avenue, New York, NY 10021, USA.
authors.forename: Natacha
authors.initials: N
authors.lastname: Opalka
authors.forename: Roland
authors.initials: R
authors.lastname: Beckmann
authors.forename: Nicolas
authors.initials: N
authors.lastname: Boisset
authors.forename: Martha N
authors.initials: MN
authors.lastname: Simon
authors.forename: Marjorie
authors.initials: M
authors.lastname: Russel
authors.forename: Seth A
authors.initials: SA
authors.lastname: Darst
mesh_terms: D020285:Cryoelectron Microscopy; D003545:Cysteine / Q000378:metabolism; D017912:Inovirus / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D009154:Mutation; D020836:Protein Structure, Quaternary; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D017361:Viral Nonstructural Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D021122:Protein Subunits; D017361:Viral Nonstructural Proteins; C119520:pIV protein, Enterobacteria phage f1; D003545:Cysteine