Processing of Transmission Electron Microscopy Images for Single-Particle Analysis of Macromolecular Complexes

International audienceThree-dimensional (3D) structure of a wide range of biological macromolecular assemblies can be computed from two-dimensional images collected by transmission electron microscopy. This information integrated with other structural data (e.g., from X-ray crystallography or nuclear magnetic resonance) helps structural biologists understand the function of macromolecular complexes. Single-particle analysis (SPA) is a method used for studies of complexes whose structure and dynamics can be analyzed in isolation. To reconstruct the 3D structure, SPA methods use a large number of images of randomly oriented individual complexes. When the angular distribution of single-particle orientations samples Fourier space completely and the population is structurally homogeneous, a resolution of the reconstruction of 0.4-1 nm can be achieved. Such high resolutions are possible thanks to the high number of images and the correction of the Contrast Transfer Function (CTF) of the microscope. One of the standard SPA approaches is the refinement of a preliminary 3D model using iterative projection matching combined with CTF correction. We describe a protocol for the refinement of a preliminary model using CTF correction by Wiener filtering of volumes from focal series of experimental images. This protocol combines potentially best features of two other protocols proposed in the field

First Neisseria gonorrhoeae Genotyping Analysis in France: Identification of a Strain Cluster with Reduced Susceptibility to Ceftriaxone ▿

Sexually transmitted infections are a major public health problem in France and other European countries. Particularly, surveillance data about Neisseria gonorrhoeae infections have clearly indicated an increase in the incidence of gonorrhoea in France in 2006. The French laboratories participated on voluntary basis in the RENAGO (Réseau National du Gonocoque) network and sent all of their collected strains to the National Reference Center for Neisseria gonorrhoeae. In this first French molecular epidemiological study, 93 isolates collected in 2006 and representative of the French gonorrhoea epidemiology were selected. Antibiotic susceptibility to six antibiotics was determined, and serotyping and N. gonorrhoeae multiantigen sequence typing (NG-MAST) were performed. NG-MAST identified 53 sequence types (STs), of which 13 STs contained 2 to 16 isolates. The major STs identified in France were previously described elsewhere. However, two newly described STs, ST1479 and ST1987, had only been found in France until now. ST1479 was characterized by a multiple-resistance phenotype, whereas ST1987 presented a susceptibility phenotype. Moreover, among the predominant French STs, ST225, which had already been described in many countries, comprised isolates (14/16) resistant to ciprofloxacin and with reduced susceptibility to ceftriaxone. Thus, the surveillance of resistance to antibiotics is a priority in order to adapt treatment and decrease the transmission of resistant strains. Of note, no predominant ST was identified among rectal isolates from men who have sex with men