Although viral protein structure and replication mechanisms have been explored extensively with X-ray crystallography, cryo-electron microscopy, and population imaging studies, these methods are often not able to distinguish dynamic conformational changes in real time. Single-molecule fluorescence resonance energy transfer (smFRET) offers unique insights into interactions and states that may be missed in ensemble studies, such as nucleic acid or protein structure, and conformational transitions during folding, receptor–ligand interactions, and fusion. We discuss the application of smFRET to the study of viral protein conformational dynamics, with a particular focus on viral glycoprotein dynamics, viral helicases, proteins involved in HIV reverse transcription, and the influenza RNA polymerase. smFRET experiments have played a crucial role in deciphering conformational changes in these processes, emphasising the importance of smFRET as a tool to help elucidate the life cycle of viral pathogens and identify key anti-viral targets.

The glial fibrillary acidic protein (GFAP) is an intermediate filament widely used to identify and label astroglial cells, a very abundant and relevant glial cell type in the central nervous system. A major hurdle in studying its behavior and function arises from the fact that GFAP does not tolerate well the addition of protein tags to its termini. Here, we tagged human GFAP (hGFAP) with an enhanced green fluorescent protein (EGFP) for the first time, and substituted a previously reported EGFP tag on mouse GFAP (mGFAP) by a more versatile Halo Tag. Both versions of tagged GFAP were able to incorporate into the normal GFAP filamentous network in glioma cells, and Alexander disease-related mutations or pharmacological disruption of microtubules and actin filaments interfered with GFAP dynamics. These new tools could provide new fruitful venues for the study of GFAP oligomerization, aggregation and dynamics in living cells.

Light emitted by molecules embedded within metal nanoparticle clusters is strongly enhanced by interaction with surface plasmons. This allows, for example, the observation of Raman scattering from individual molecules. The symmetry of the metal cluster may affect the Raman-scattered light by generating new polarization states. This article reviews the use of symmetry theory to analyze the plasmonic normal modes of metal nanoparticle trimers. The lowest bright energy modes are degenerate for an equilateral triangle but split when the symmetry is broken. When a single molecule in the gap between two of the particles emits, it excites the plasmon modes, typically off-resonance, and the ensuing interference between the modes rotates the polarization of the emitted light. This so-called Raman optical activity can generate circularly polarized light at the Raman frequency. This curious phenomenon, which was demonstrated experimentally, may prove useful for future plasmonic devices.