Structure and function of the components of the core of the T7 bacteriophage, a DNA translocation comples

• Autores: María Pérez
• Directores de la Tesis: José López Carrascosa (dir. tes.), Ana Maria Cuervo (codir. tes.)
• Lectura: En la Universidad Autónoma de Madrid ( España ) en 2019
• Idioma: inglés
• Títulos paralelos:
  • Estructura y función de los componentes del core del bacteriófago t7, un complejo de translación del ADN
• Tribunal Calificador de la Tesis: Carmen San Martín Pastrana (presid.), José María Carazo García (secret.), Juan Fontana Jordán de Urríes (voc.)
• Programa de doctorado: Programa de Doctorado en Biología por la Universidad Autónoma de Madrid
• Materias:
  • Física
    • Electrónica
      • Microscopia electrónica
  • Ciencias de la vida
    • Virología
      • Bacteriófagos
• Enlaces
  • Tesis en acceso abierto en: Biblos-e Archivo
• Resumen

  • Transport of the viral DNA genome trough cell membranes is still one of the most intriguing processes in bacteriophage life cycle. In most of the bacterial viruses this process is carried out by the tail machinery, which shares structural similarities with bacterial secretion systems. However, some viruses present a tail, which is too short to puncture the bacterial cell wall. T7 bacteriophage, a member of the Podoviridae family, presents a short and non-contractile tail and it is an interesting system to study how these viruses puncture the double membranes of E. coli gram-negative bacteria. In order to enlarge the tail complex, it has been postulated that during infection, an internal head complex, the core, is translocated trough the tail channel and assembles a tubular structure in the periplasm that allows the viral DNA translocation.

    In this work, we have cloned and purified gp15 and gp16 core proteins. Both proteins were able to interact in vitro and we have solved the structure of two different core assemblies, gp15 alone and in complex with gp16, by cryo-EM at near-atomic resolution (3.64 and 3.18 Å). These structures show for the first time that T7 core proteins are able to form tubular structures. A special feature of these structures is that they seem to present partially folded domains, whose density is not observed in the reconstructions. Moreover, the formation of the gp15-gp16 complex allows the complete folding of gp15, suggesting that gp16 acts as a chaperone assisting the assembly of the translocation complex. The solved domain of gp16 also shows a transglycosylase canonical motif, which could be involved in the degradation of peptidoglycan layer of E. coli.

    The study of the T7 core complex inside the capsid was performed using cryo-EM and a special data processing of this mismatched symmetry complex, which allowed us to obtain a core-tail complex model at 4.84 Å resolution.

    Altogether, our results suggest that the interaction of gp15 and gp16 core proteins show a novel type of assisted folding and allowed us to propose an assembly process.