Dengue, West Nile and Zika, closely related viruses of the Flaviviridae family, are an increasing global threat, due to the expansion of their mosquito vectors. They present a very similar viral particle with an outer lipid bilayer containing two viral proteins and, within it, the nucleocapsid core. This core is composed by the viral RNA complexed with multiple copies of the capsid protein, a crucial structural protein that mediates not only viral assembly, but also encapsidation, by interacting with host lipid systems. The capsid is a homodimeric protein that contains a disordered N-terminal region, an intermediate flexible fold section and a very stable conserved fold region. Since a better understanding of its structure can give light into its biological activity, here, first, we compared and analyzed relevant mosquito-borne Flavivirus capsid protein sequences and their predicted structures. Then, we studied the alternative conformations enabled by the N-terminal region. Finally, using dengue virus capsid protein as main model, we correlated the protein size, thermal stability and function with its structure/dynamics features. The findings suggest that the capsid protein interaction with host lipid systems leads to minor allosteric changes that may modulate the specific binding of the protein to the viral RNA. Such mechanism can be targeted in future drug development strategies, namely by using improved versions of pep14-23, a dengue virus capsid protein peptide inhibitor, previously developed by us. Such knowledge can yield promising advances against Zika, dengue and closely related Flavivirus.

Gangliosides are glycosphingolipids consisting of a ceramide base and a bulky sugar chain that contains one or more sialic acids. This unique structure endows gangliosides with a strong tendency to self‐aggregate in solution, as well as in cellular membranes, where they can form nanoscopic assemblies called ganglioside nanodomains. As gangliosides are important biological molecules involved in a number of physiological processes, characterization of their lateral organization in membranes is essential. This review aims at providing comprehensive information about the nanoscale organization of gangliosides in various synthetic models. To this end, the impact of the hydrophobic backbone and the headgroup on the segregation of gangliosides into nanodomains are discussed in detail, as well as the way in which the properties of nanodomains are affected by ligand binding. Small size makes the characterization of ganglioside nanodomains challenging, and we thus highlight the biophysical methods that have advanced this research, such as Monte Carlo Förster resonance energy transfer, atomic force microscopy and approaches based on molecular diffusion.

Galectin-1 (Gal-1) is a galactose-binding protein involved in various cellular functions. Gal-1’s activity has been suggested to be connected to two molecular concepts, which are, however, lacking experimental proof: a) enhanced binding affinity of Gal-1 toward membranes containing monosialotetrahexosylganglioside (GM₁) over disialoganglioside GD₁a and b) cross-linking of GM₁’s by homodimers of Gal-1. We provide evidence about the specificity and the nature of the interaction of Gal-1 with model membranes containing GM₁ or GD₁a, employing a broad panel of fluorescence-based and label-free experimental techniques, complemented by atomistic biomolecular simulations. Our study demonstrates that Gal-1 indeed binds specifically to GM₁ and not to GD₁a when embedded in membranes over a wide range of concentrations (i.e., 30 nM to 20 μM). The apparent binding constant is about tens of micromoles. On the other hand, no evidence of Gal-1/GM₁ cross-linking was observed. Our findings suggest that cross-linking does not result from sole interactions between GM₁ and Gal-1, indicating that in a physiological context, additional triggers are needed, which shift the GM₁/Gal-1 equilibria toward the membrane-bound homodimeric Gal-1.

Galectin-1 (Gal-1) is a galactose-binding protein involved in various cellular functions. Gal-1’s activity has been suggested to be connected to two molecular concepts, which are however lacking experimental proof: a) enhanced binding affinity of Gal-1 towards membranes containing monosialotetrahexosylganglioside (GM ₁ ) over disialoganglioside GD ₁ a and b) cross-linking of GM ₁ ’s by homodimers of Gal-1. We provide evidence about the specificity and the nature of Gal-1 interaction with model membranes containing GM ₁ or GD ₁ a, employing a broad panel of fluorescence-based and label-free experimental techniques, complemented by atomistic biomolecular simulations. Our study demonstrates that Gal-1 binds indeed specifically to GM ₁ , and not to GD ₁ a, when embedded in membranes over a wide range of concentrations (i.e., 30 nM to 10 μM). The apparent binding constant is about tens of micromoles. On the other hand, no evidence of Gal-1/GM ₁ cross-linking was observed. Our findings suggest that cross-linking does not result from sole interactions between GM ₁ and Gal-1, indicating that in a physiological context, additional triggers are needed, which shift the GM ₁ /Gal-1 equilibria towards the membrane-bound homodimeric Gal-1. Abstract Figure: