title: Bacteriophage T5 structure reveals similarities with HK97 and T4 suggesting evolutionary relationships.
abstract: Evolutionary relationships between viruses may be obscure by protein sequence but unmasked by structure. Analysis of bacteriophage T5 by cryo-electron microscopy and protein sequence analysis reveals analogies with HK97 and T4 that suggest a mosaic of such connections. The T5 capsid is consistent with the HK97 capsid protein fold but has a different geometry, incorporating three additional hexamers on each icosahedral facet. Similarly to HK97, the T5 major capsid protein has an N-terminal extension, or Delta-domain that is missing in the mature capsid, and by analogy with HK97, may function as an assembly or scaffold domain. This Delta-domain is predicted to be largely coiled-coil, as for that of HK97, but is approximately 70% longer correlating with the larger capsid. Thus, capsid architecture appears likely to be specified by the Delta-domain. Unlike HK97, the T5 capsid binds a decoration protein in the center of each hexamer similarly to the "hoc" protein of phage T4, suggesting a common role for these molecules. The tail-tube has unusual trimeric symmetry that may aid in the unique two-stage DNA-ejection process, and joins the tail-tip at a disk where tail fibers attach. This intriguing mix of characteristics embodied by phage T5 offers insights into virus assembly, subunit function, and the evolutionary connections between related viruses.
authors.affiliation: Laboratoire de Microscopie Electronique Structurale, Institut de Biologie Structurale J.-P. Ebel, UMR 5075 CNRS-CEA-UJF, 38027 Grenoble, France.
authors.forename: G
authors.initials: G
authors.lastname: Effantin
authors.forename: P
authors.initials: P
authors.lastname: Boulanger
authors.forename: E
authors.initials: E
authors.lastname: Neumann
authors.forename: L
authors.initials: L
authors.lastname: Letellier
authors.forename: J F
authors.initials: JF
authors.lastname: Conway
mesh_terms: D000595:Amino Acid Sequence; D017122:Bacteriophage T4 / Q000737:chemistry* / Q000648:ultrastructure*; D002213:Capsid / Q000737:chemistry; D036022:Capsid Proteins / Q000737:chemistry*; D020285:Cryoelectron Microscopy; D019143:Evolution, Molecular; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017386:Sequence Homology, Amino Acid; D017906:Siphoviridae / Q000737:chemistry* / Q000648:ultrastructure*
chemical_list: D036022:Capsid Proteins