title: In vivo bypass of chaperone by extended coiled-coil motif in T4 tail fiber.
abstract: The distal-half tail fiber of bacteriophage T4 is made of three gene products: trimeric gp36 and gp37 and monomeric gp35. Chaperone P38 is normally required for folding gp37 peptides into a P37 trimer; however, a temperature-sensitive mutation in T4 (ts3813) that suppresses this requirement at 30 degrees C but not at 42 degrees C was found in gene 37 (R. J. Bishop and W. B. Wood, Virology 72:244-254, 1976). Sequencing of the temperature-sensitive mutant revealed a 21-bp duplication of wild-type gene 37 inserted into its C-terminal portion (S. Hashemolhosseini et al., J. Mol. Biol. 241:524-533, 1994). We noticed that the 21-amino-acid segment encompassing this duplication in the ts3813 mutant has a sequence typical of a coiled coil and hypothesized that its extension would relieve the temperature sensitivity of the ts3813 mutation. To test our hypothesis, we crossed the T4 ts3813 mutant with a plasmid encoding an engineered pentaheptad coiled coil. Each of the six mutants that we examined retained two amber mutations in gene 38 and had a different coiled-coil sequence varying from three to five heptads. While the sequences varied, all maintained the heptad-repeating coiled-coil motif and produced plaques at up to 50 degrees C. This finding strongly suggests that the coiled-coil motif is a critical factor in the folding of gp37. The presence of a terminal coiled-coil-like sequence in the tail fiber genes of 17 additional T-even phages implies the conservation of this mechanism. The increased melting temperature should be useful for "clamps" to initiate the folding of trimeric beta-helices in vitro and as an in vivo screen to identify, sequence, and characterize trimeric coiled coils.
authors.affiliation: Tufts University School of Medicine, Dept. of Molecular and Microbiology, 146 Harrison Ave., Boston, MA 02111, USA.
authors.forename: Yun
authors.initials: Y
authors.lastname: Qu
authors.forename: Paul
authors.initials: P
authors.lastname: Hyman
authors.forename: Timothy
authors.initials: T
authors.lastname: Harrah
authors.forename: Edward
authors.initials: E
authors.lastname: Goldberg
mesh_terms: D000595:Amino Acid Sequence; D017122:Bacteriophage T4 / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D015967:Gene Expression Regulation, Viral; D018832:Molecular Chaperones / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D011487:Protein Conformation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D013696:Temperature; D017376:Viral Tail Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: D018832:Molecular Chaperones; D017376:Viral Tail Proteins