Nanoscale structural response of ganglioside-containing aggregates to the interaction with sialidase.

It is well known that the curvature of ganglioside-containing nanoparticles strongly depends on their headgroup structure, as determined in aggregates with 'stationary' composition, that is, when the system finds its optimal structure at the moment of lipid dissolution in aqueous solution. In the present work, we directly followed the structural change in model aggregates, induced by on-line molecular modification of already-packed gangliosides, namely the one brought about by a sialidase, acting on the ganglioside GD1a and leading to the lower-curvature-aggregating GM1. We applied small-angle X-ray and neutron scattering techniques to follow the time evolution of the aggregate structure. We found that, while chemically undergoing the enzymatic action in both cases, the aggregated structure could be either very stable, in single component systems, or structurally responsive, in mixed model systems. Moreover, while in progress, the sialidase-ganglioside interaction seems to define a time lag where the system is structurally off the smooth route between the initial and the final states. We hypothesize that, in this time lag, the local structure could be very sensitive to the environment and eventually readdressed to a specific final structural fate.