Food-grade titanium dioxide translocates across the buccal mucosa in pigs and induces genotoxicity in an model of human oral epithelium.

The whitening and opacifying agent titanium dioxide (TiO) is used worldwide in various foodstuffs, toothpastes and pharmaceutical tablets. Its use as a food additive (E171 in EU) has raised concerns for human health. Although the buccal mucosa is the first area exposed, oral transmucosal passage of TiO particles has not been documented.

npSCOPE: A New Multimodal Instrument for In Situ Correlative Analysis of Nanoparticles.

Over the last few decades, nanoparticles have become a key element in a number of scientific and technological fields, spanning from materials science to life sciences. The characterization of nanoparticles or samples containing nanoparticles, in terms of morphology, chemical composition, and other parameters, typically involves investigations with various analytical tools, requiring complex workflows and extending the duration of such studies to several days or even weeks. Here, we report on the development of a new unique in situ correlative instrument, allowing us to answer questions about the shape, size, size distribution, and chemical composition of the nanoparticles using a single probe.

New hardware and workflows for semi-automated correlative cryo-fluorescence and cryo-electron microscopy/tomography.

Correlative light and electron microscopy allows features of interest defined by fluorescence signals to be located in an electron micrograph of the same sample. Rare dynamic events or specific objects can be identified, targeted and imaged by electron microscopy or tomography. To combine it with structural studies using cryo-electron microscopy or tomography, fluorescence microscopy must be performed while maintaining the specimen vitrified at liquid-nitrogen temperatures and in a dry environment during imaging and transfer.

X-ray and Cryo-electron Microscopy Structures of Monalysin Pore-forming Toxin Reveal Multimerization of the Pro-form.

β-Barrel pore-forming toxins (β-PFT), a large family of bacterial toxins, are generally secreted as water-soluble monomers and can form oligomeric pores in membranes following proteolytic cleavage and interaction with cell surface receptors. Monalysin has been recently identified as a β-PFT that contributes to the virulence of Pseudomonas entomophila against Drosophila. It is secreted as a pro-protein that becomes active upon cleavage.

Cryo-electron microscopy structure of lactococcal siphophage 1358 virion.

Unlabelled: Lactococcus lactis, a Gram(+) lactic acid-producing bacterium used for the manufacture of several fermented dairy products, is subject to infection by diverse virulent tailed phages, leading to industrial fermentation failures. This constant viral risk has led to a sustained interest in the study of their biology, diversity, and evolution. Lactococcal phages now constitute a wide ensemble of at least 10 distinct genotypes within the Caudovirales order, many of them belonging to the Siphoviridae family.

Inter-ring rotations of AAA ATPase p97 revealed by electron cryomicroscopy.

The type II AAA+ protein p97 is involved in numerous cellular activities, including endoplasmic reticulum-associated degradation, transcription activation, membrane fusion and cell-cycle control. These activities are at least in part regulated by the ubiquitin system, in which p97 is thought to target ubiquitylated protein substrates within macromolecular complexes and assist in their extraction or disassembly. Although ATPase activity is essential for p97 function, little is known about how ATP binding or hydrolysis is coupled with p97 conformational changes and substrate remodelling.

Structures and host-adhesion mechanisms of lactococcal siphophages.

The Siphoviridae family of bacteriophages is the largest viral family on earth and comprises members infecting both bacteria and archaea. Lactococcal siphophages infect the Gram-positive bacterium Lactococcus lactis, which is widely used for industrial milk fermentation processes (e.g.

Structure, adsorption to host, and infection mechanism of virulent lactococcal phage p2.

Lactococcal siphophages from the 936 and P335 groups infect the Gram-positive bacterium Lactococcus lactis using receptor binding proteins (RBPs) attached to their baseplate, a large multiprotein complex at the distal part of the tail. We have previously reported the crystal and electron microscopy (EM) structures of the baseplates of phages p2 (936 group) and TP901-1 (P335 group) as well as the full EM structure of the TP901-1 virion. Here, we report the complete EM structure of siphophage p2, including its capsid, connector complex, tail, and baseplate.

TssK is a trimeric cytoplasmic protein interacting with components of both phage-like and membrane anchoring complexes of the type VI secretion system.

The Type VI secretion system (T6SS) is a macromolecular machine that mediates bacteria-host or bacteria-bacteria interactions. The T6SS core apparatus assembles from 13 proteins that form two sub-assemblies: a phage-like complex and a trans-envelope complex. The Hcp, VgrG, TssE, and TssB/C subunits are structurally and functionally related to components of the tail of contractile bacteriophages.

Structure and functional analysis of the host recognition device of lactococcal phage tuc2009.

Many phages employ a large heteropolymeric organelle located at the tip of the tail, termed the baseplate, for host recognition. Contrast electron microscopy (EM) of the lactococcal phage Tuc2009 baseplate and its host-binding subunits, the so-called tripods, allowed us to obtain a low-resolution structural image of this organelle. Structural comparisons between the baseplate of the related phage TP901-1 and that of Tuc2009 demonstrated that they are highly similar, except for the presence of an additional protein in the Tuc2009 baseplate (BppATuc2009), which is attached to the top of the Tuc2009 tripod structure.

X-ray structure of a superinfection exclusion lipoprotein from phage TP-J34 and identification of the tape measure protein as its target.

Lipoproteins of temperate phage are a broad family of membrane proteins encoded in the lysogeny module of temperate phages. Expression of the ltp(TP-J34) gene of temperate Streptococcus thermophilus phage TP-J34 interferes with phage infection at the stage of triggering DNA release and injection into the cell. Here, we report the first structure of a superinfection exclusion protein.

The first structure of a mycobacteriophage, the Mycobacterium abscessus subsp. bolletii phage Araucaria.

The unique characteristics of the waxy mycobacterial cell wall raise questions about specific structural features of their bacteriophages. No structure of any mycobacteriophage is available, although ∼3,500 have been described to date. To fill this gap, we embarked in a genomic and structural study of a bacteriophage from Mycobacterium abscessus subsp.

Viral infection modulation and neutralization by camelid nanobodies.

Lactococcal phages belong to a large family of Siphoviridae and infect Lactococcus lactis, a gram-positive bacterium used in commercial dairy fermentations. These phages are believed to recognize and bind specifically to pellicle polysaccharides covering the entire bacterium. The phage TP901-1 baseplate, located at the tip of the tail, harbors 18 trimeric receptor binding proteins (RBPs) promoting adhesion to a specific lactococcal strain.

Visualizing a complete Siphoviridae member by single-particle electron microscopy: the structure of lactococcal phage TP901-1.

Tailed phages are genome delivery machines exhibiting unequaled efficiency acquired over more than 3 billion years of evolution. Siphophages from the P335 and 936 families infect the Gram-positive bacterium Lactococcus lactis using receptor-binding proteins anchored to the host adsorption apparatus (baseplate). Crystallographic and electron microscopy (EM) studies have shed light on the distinct adsorption strategies used by phages of these two families, suggesting that they might also rely on different infection mechanisms.

Distinct conformations of the protein complex p97-Ufd1-Npl4 revealed by electron cryomicroscopy.

p97 is a key regulator of numerous cellular pathways and associates with ubiquitin-binding adaptors to remodel ubiquitin-modified substrate proteins. How adaptor binding to p97 is coordinated and how adaptors contribute to substrate remodeling is unclear. Here we present the 3D electron cryomicroscopy reconstructions of the major Ufd1-Npl4 adaptor in complex with p97.

Structure and molecular assignment of lactococcal phage TP901-1 baseplate.

P335 lactococcal phages infect the gram(+) bacterium Lactococcus lactis using a large multiprotein complex located at the distal part of the tail and termed baseplate (BP). The BP harbors the receptor-binding proteins (RBPs), which allow the specific recognition of saccharidic receptors localized on the host cell surface. We report here the electron microscopic structure of the phage TP901-1 wild-type BP as well as those of two mutants bppL (-) and bppU(-), lacking BppL (the RBPs) or both peripheral BP components (BppL and BppU), respectively.

Structure of lactococcal phage p2 baseplate and its mechanism of activation.

Siphoviridae is the most abundant viral family on earth which infects bacteria as well as archaea. All known siphophages infecting gram+ Lactococcus lactis possess a baseplate at the tip of their tail involved in host recognition and attachment. Here, we report analysis of the p2 phage baseplate structure by X-ray crystallography and electron microscopy and propose a mechanism for the baseplate activation during attachment to the host cell.