title: The NMR structure of the gpU tail-terminator protein from bacteriophage lambda: identification of sites contributing to Mg(II)-mediated oligomerization and biological function.
abstract: During the late stages of lambda bacteriophage assembly, the protein gpU terminates tail polymerization and participates at the interface between the mature capsid and tail components. When it engages the lambda tail, gpU undergoes a monomer-hexamer transition to achieve its biologically active form. Towards understanding how gpU participates in multiple protein-protein interactions, we have solved the structure of gpU in its monomeric state using NMR methods. The structure reveals a mixed alpha/beta motif with several dynamic loops at the periphery. Addition of 20 mM MgCl(2) is known to oligomerize gpU in the absence of its protein partners. Multiple image analysis of electron micrographs revealed ring-like structures of magnesium ion saturated gpU with a 30 A pore, consistent with its function as a portal for the passage of viral DNA into the host bacterium. The ability of magnesium ions to promote oligomerization was lost when substitutions were made at a cluster of acidic amino acids in the vicinity of helix alpha2 and the beta1-beta2 loop. Furthermore, substitutions at these sites abolished the biological activity of gpU.
authors.affiliation: Department of Biology, York University, 4700 Keele Street, Canada M3J 1P3.
authors.forename: Lizbeth
authors.initials: L
authors.lastname: Edmonds
authors.forename: Amanda
authors.initials: A
authors.lastname: Liu
authors.forename: Jamie J
authors.initials: JJ
authors.lastname: Kwan
authors.forename: Aida
authors.initials: A
authors.lastname: Avanessy
authors.forename: Mary
authors.initials: M
authors.lastname: Caracoglia
authors.forename: Irene
authors.initials: I
authors.lastname: Yang
authors.forename: Karen L
authors.initials: KL
authors.lastname: Maxwell
authors.forename: John
authors.initials: J
authors.lastname: Rubenstein
authors.forename: Alan R
authors.initials: AR
authors.lastname: Davidson
authors.forename: Logan W
authors.initials: LW
authors.lastname: Donaldson
mesh_terms: D000595:Amino Acid Sequence; D010582:Bacteriophage lambda / Q000737:chemistry* / Q000378:metabolism; D008274:Magnesium / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016296:Mutagenesis; D019906:Nuclear Magnetic Resonance, Biomolecular; D011487:Protein Conformation; D016415:Sequence Alignment; D014764:Viral Proteins / Q000737:chemistry* / Q000378:metabolism* / Q000648:ultrastructure; D019065:Virus Assembly
chemical_list: D014764:Viral Proteins; D008274:Magnesium