A new optical microscopy approach opens the door to better observations in molecular biology

Researchers from the Institut Pasteur and CNRS have set up a new optical microscopy approach that combines two recent imaging techniques in order to visualise molecular assemblies without affecting their biological functions, at a resolution 10 times better than that of traditional microscopes.

Using this approach, they were able to observe the AIDS virus and its capsids (containing the HIV genome) within cells at a scale of 30 nanometres, for the first time with light.

This newly developed approach represents a significant advance in molecular biology, opening the door to less invasive and more precise analyses of pathogenic microorganisms present in human host cells. This study is already published in the Electronic Edition of PNAS.

It has always been necessary for researchers to visualise pathogenic microorganisms in their host cell's environment, in order to define the host-pathogen interactions contributing to viral infections. Optical microscopy, combined with fluorescent labels (such as GFP proteins and antibodies coupled with synthetic fluorophores), allows to showcase the specific structures of cells, including proteins.

However, this approach is limited by its low resolving power, which only helps distinguish cellular and molecular structures at a scale of 200-300 nanometres (nm). Most pathogenic viruses are of smaller sizes. Consequently, it is essential to resort to more precise imaging techniques, in order to better understand and define the internal structure of such viruses.
 
A study coordinated by Dr Christophe Zimmer, head of the computational imaging and modelling group  (Institut Pasteur / CNRS), in collaboration with Dr Nathalie Arhel, molecular virology and vaccinology unit (Institut Pasteur / CNRS), within the lab headed by Prof Pierre Charneau, head of the molecular virology and vaccinology unit,  (Institut Pasteur / CNRS), shows that the association of two recent imaging techniques helps obtain unique images of molecular assemblies of HIV-1 capsids, with a resolution around 10 times better than that of traditional microscopes.

This new approach, which uses super-resolution imaging and FlAsH labelling, does not affect the virus' ability to self-replicate. It represents a major step forward in molecular biology studies, enabling the visualisation of microbial complexes at a scale of 30 nm without affecting their function.
 
The newly developed approach combines super-resolution PALM imaging and fluorescent FlAsH labeling. PALM imaging relies on the acquisition of thousands of low-resolution images, each of which showing only a few fluorescent molecules.