Dynamic force microscopy for imaging of viruses under physiological conditions

Dynamic force microscopy (DFM) allows imaging of the structure and the assessment of the function of biological specimens in their physiological environment. In DFM, the cantilever is oscillated at a given frequency and touches the sample only at the end of its downward movement. Accordingly, the problem of lateral forces displacing or even destroying bio-molecules is virtually inexistent as the contact time and friction forces are reduced. Here, we describe the use of DFM in studies of human rhinovirus serotype 2 (HRV2) weakly adhering to mica surfaces. The capsid of HRV2 was reproducibly imaged without any displacement of the virus. Release of the genomic RNA from the virions was initiated by exposure to low pH buffer and snapshots of the extrusion process were obtained. In the following, the technical details of previous DFM investigations of HRV2 are summarized

X-ray structure of a minor group human rhinovirus bound to a fragment of its cellular receptor protein

Although many viral receptors have been identified, the ways in which they interact with their cognate viruses are not understood at the molecular level. We have determined the X-ray structure of a complex between calcium-containing modules of the very low-density lipoprotein receptor and the minor group human rhinovirus HRV2. The receptor binds close to the icosahedral five-fold vertex, with only one module per virus protomer. The binding face of this module is defined by acidic calcium-chelating residues and, in particular, by an exposed tryptophan that is highly conserved. The attachment site on the virus involves only residues from VP1, particularly a lysine strictly conserved in all minor group HRVs. The disposition of the attached ligand-binding repeats around the five-fold axis, together with the proximity of the N- and C-terminal ends of adjacent modules, suggests that more than one repeat in a single receptor molecule might attach simultaneously.Peer Reviewe

Neutralization of a common cold virus by concatemers of the third ligand binding module of the VLDL-receptor strongly depends on the number of modules

Concatemers of various numbers of the third ligand binding repeat of human very-low density lipoprotein receptor arranged in tandem were fused to maltose-binding protein and expressed as soluble polypeptides. These artificial receptors protected HeLa cells against infection with human rhinovirus serotype 2 (HRV2) to a degree that strongly increased with the number of repeats present; maximal protection was seen for the pentameric concatemer (MBP-V33333). This V3 pentamer neutralized HRV2 more efficiently than a recombinant protein with the entire ligand binding domain of the native receptor encompassing all 8 non-identical repeats. A concatemer of seven V3 modules (MBP-V3333333) was also less neutralizing. Neutralization was correlated with the degree of inhibition of virus binding to the cell surface. The results were in agreement with kinetic measurements using Biacore instrumentation demonstrating an increase in avidity with the number of modules present. At low concentrations of the receptor fragments, a 1:1 Langmuir kinetics was observed which became of complex type in the higher concentration range. This is most likely a consequence of receptor molecules simultaneously binding via several modules. Since there is no viral aggregation, neutralization of viral infectivity results from blockage of the receptor binding sites and possibly from inhibition of viral uncoating by crosslinking the viral capsid subunits via multi-module binding. Finally, the low affinity of the single V3 module allowed demonstrating the possibility of mapping the binding epitope of the V3 receptor fragment by saturation transfer difference nuclear magnetic resonance methodology

Langues et migrations

Ce dossier explore les réalités de la pluralité linguistique, qu'elle soit pratiquée dans les familles immigrées ou bien encouragée à travers des programmes d'enseignement, des actions sociales et culturelles, et dans les créations littéraires. La dimension comparative permet de comprendre comment se combinent les usages des langues dans plusieurs contextes géographiques, en Europe et aussi au Québec. Ce dossier est coordonné par la Délégation générale à la langue de France (ministère de la Culture et de la Communication), avec la participation de l'Observatoire des pratiques linguistiques