31 research outputs found
Structural and mechanistic insights into the bacterial amyloid secretion channel CsgG
Curli are functional amyloid fibres that constitute the major protein component of the extracellular matrix in pellicle biofilms formed by Bacteroidetes and Proteobacteria (predominantly of the α and γ classes). They provide a fitness advantage in pathogenic strains and induce a strong pro-inflammatory response during bacteraemia. Curli formation requires a dedicated protein secretion machinery comprising the outer membrane lipoprotein CsgG and two soluble accessory proteins, CsgE and CsgF. Here we report the X-ray structure of Escherichia coli CsgG in a non-lipidated, soluble form as well as in its native membrane-extracted conformation. CsgG forms an oligomeric transport complex composed of nine anticodon-binding-domain-like units that give rise to a 36-stranded β-barrel that traverses the bilayer and is connected to a cage-like vestibule in the periplasm. The transmembrane and periplasmic domains are separated by a 0.9-nm channel constriction composed of three stacked concentric phenylalanine, asparagine and tyrosine rings that may guide the extended polypeptide substrate through the secretion pore. The specificity factor CsgE forms a nonameric adaptor that binds and closes off the periplasmic face of the secretion channel, creating a 24,000 Å(3) pre-constriction chamber. Our structural, functional and electrophysiological analyses imply that CsgG is an ungated, non-selective protein secretion channel that is expected to employ a diffusion-based, entropy-driven transport mechanism
Paragraph development : a guide for students of english as a second language / Martin L. Arnaudet
x,193 hlm.; 24 cm
Sophrolipids : a yeast-derived glycolipid as greener structure directing agents for self-assembled nanomaterials.
International audienceSophorolipids, fully natural glycolipids, can form in water nanometre-size micelles of various geometries depending on their concentration as shown by small angle neutron scattering experiments. This property allows use of them, for the first time, as structure directing agents in the synthesis of nanostructured silica thin films via the evaporation induced self-assembly (EISA) process
Supramolecular Organization and siRNA Binding of Hyaluronic Acid-Coated Lipoplexes for Targeted Delivery to the CD44 Receptor
The dynamics of the formation of
siRNA-lipoplexes coated with hyaluronic
acid (HA) and the parameters influencing their supramolecular organization
were studied. The insertion of a HA-dioleylphosphatidylethanolamine
(DOPE) conjugate in the liposome structure as well as subsequent complexation
with siRNA increased the liposome size. Lipoplexes were around 110
nm at high ± charge ratios with a zeta potential around +50 mV
and around 230 nm at low ± ratios, with a zeta potential that
decreased to negative values, reaching −45 mV. The addition
of the conjugate did not compromise siRNA binding to liposomes, although
these nucleic acids induced a displacement of part of the HA-DOPE
conjugate upon lipoplex formation, as confirmed by capillary electrophoresis.
Isothermal titration calorimetry, X-ray diffraction studies, and cryo-TEM
microscopy demonstrated that in addition to electrostatic interactions
with siRNA a rearrangement of the lipid bilayers takes place, resulting
in condensed oligolamellar vesicles. This phenomenon is dependent
on the number of siRNA molecules and the degree of modification with
HA. Finally, the suitable positioning of HA on the lipoplex surface
and its ability to bind specifically to the CD44 receptors in a concentration-dependent
manner was demonstrated by surface plasmon resonance analysis