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Langlois, C, Ramboarina, S, Cukkemane, A, Auzat, I, Chagot, B, Gilquin, B, Ignatiou, A, Petitpas, I, Kasotakis, E, Paternostre, M, White, HE, Orlova, EV, Baldus, M, Tavares, P and Zinn-Justin, S (2015) Bacteriophage SPP1 tail tube protein self-assembles into β-structure-rich tubes. J. Biol. Chem. 290:3836-49
The majority of known bacteriophages have long tails that serve for bacterial target recognition and viral DNA delivery into the host. These structures form a tube from the viral capsid to the bacterial cell. The tube is formed primarily by a helical array of tail tube protein (TTP) subunits. In phages with a contractile tail, the TTP tube is surrounded by a sheath structure. Here, we report the first evidence that a phage TTP, gp17.1 of siphophage SPP1, self-assembles into long tubes in the absence of other viral proteins. gp17.1 does not exhibit a stable globular structure when monomeric in solution, even if it was confidently predicted to adopt the β-sandwich fold of phage λ TTP. However, Fourier transform infrared and nuclear magnetic resonance spectroscopy analyses showed that its β-sheet content increases significantly during tube assembly, suggesting that gp17.1 acquires a stable β-sandwich fold only after self-assembly. EM analyses revealed that the tube is formed by hexameric rings stacked helicoidally with the same organization and helical parameters found for the tail of SPP1 virions. These parameters were used to build a pseudo-atomic model of the TTP tube. The large loop spanning residues 40-56 is located on the inner surface of the tube, at the interface between adjacent monomers and hexamers. In line with our structural predictions, deletion of this loop hinders gp17.1 tube assembly in vitro and interferes with SPP1 tail assembly during phage particle morphogenesis in bacteria.
Amino Acid Sequence; Bacteriophages/chemistry; Molecular Sequence Data; Protein Folding; Protein Structure, Tertiary; Viral Proteins/chemistry
|Gene product||Qualifier||GO Term||Evidence Code||with/from||Aspect||Extension||Notes||Status|
|GO:0098026: virus tail, tube||
TTP, gp17.1 has been identified to be able to self assemble into long tubes in the absence of other phage proteins. In figure 6 there is a comparison done between gp17.1 and tails of SSP1 virions that show similar morphology. These samples were negatively stained and it was observed that both gp17.1 is hollow and the empty virion tails that have ejected their DNA after incubation in a SSP1 bacterial receptor. Aligned segments of gp17.1 were taken then calculation was performed for its diffraction pattern. This pattern revealed that tubes have a 6-fold symmetry which are made by stacks of hexameric rings. These rings form helical tubes that elongate.
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