[Todos] SEMINARIO EXTRAORDINARIO QB 2014 - Lunes 15 de septiembre 11 h - Cécile Breyton

[Claudia Sepúlveda]

SEMINARIO EXTRAORDINARIO DEL DEPARTAMENTO DE QUÍMICA BIOLÓGICA

LUNES 15 de septiembre a las 11:00 h, Aula Cardini del Departamento de
Química Biológica, 4to piso.
----------------------------------------------------------------------------

Expositor: Cécile Breyton
Institute for Structural Biology, CEA, CNRS, Université Grenoble Alpes,
Grenoble, France.

"How do bacteriophages recognize and infect their hosts? Insights into the
architecture and structure of the tail of phage T5"

The tail of Caudovirales bacteriophages serves as an adsorption device, a
host cell-wall perforating machine and a genome delivery pathway. In
Siphoviridae, the assembly of the long and flexible tail is a highly
regulated process. We combined a proteomic analysis of phage T5 particles
with a bioinformatic study and electron microscopic immunolocalisation to
assign function to the structural proteins of the tail of this siphophage
infecting E. coli. We localised most of the tail proteins that were
hitherto uncharacterised, and provide a detailed description of the tail
tip composition, formed by 4 proteins only.
Infection of E. coli cells by phage T5 is triggered by the irreversible
binding of pb5, at the tip of the straight fibre, to the outer membrane
iron-ferrichrome transporter FhuA. Binding of pb5 to FhuA induces opening
of the capsid and perforation of the host cell wall. An elegant Small
Angle Neutron Scattering study, combining the use of a fluorinated
surfactant, contrast variation and deuterium labelling of proteins,
allowed us to conclude that no large conformational changes occurred upon
interaction of the two proteins. Thus, the transmission to the rest of the
phage of the binding/host recognition information occurs through secondary
structure conformational changes that we have evidenced in a biochemical
and biophysical study of the FhuA-pb5 complex.
Within the tail tip complex, the Distal tail (Dit) protein has been
structurally characterised in Gram-positive infecting siphophages. It is
organised as a hexameric ring that connects the tail tube and the
adsorption device. We characterised the protein pb9 of T5, which is
located in the upper cone of T5 tail tip, at the end of the tail tube. The
crystal structure of pb9 reveals a two-domain protein. Domain A exhibits
remarkable structural similarity with the N-terminal domain of known Dit
proteins, while domain B adopts an Oligosaccharide/ oligonucleotide
Binding-fold (OB-fold) that is not shared by these proteins. We thus
propose that pb9 is the Dit protein of T5, making it the first Dit protein
described for a Gram-negative infecting siphophage. Multiple sequence
alignments suggest that pb9 is a paradigm for a large family of Dit
proteins of siphopages infecting mostly gram-negative hosts. The modular
structure of the Dit protein maintains the basic building block that would
be conserved among all siphophages, combining it with a more divergent
domain that might serve specific host adhesion properties.
----------------------------------------------------------------------------

Los esperamos!

Martín Edreira
Diego Grinman
Diego Laderach
Claudia Sepúlveda

Organizadores de los Seminarios del Dpto. Química Biológica, FCEyN-UBA.


Puede consultarse la agenda de próximos seminarios en
http://www.qb.fcen.uba.ar/seminarios.html