Proteins are broadly versatile biochemical materials,
whose functionality
is tightly related to their folding state. Native folding can be lost
to yield misfolded conformations, often leading to formation of protein
oligomers, aggregates, and biomolecular phase condensates. The fluorogenic
hyaluronan HA-RB, a nonsulfonated glycosaminoglycan with a combination
of polyanionic character and of hydrophobic spots due to rhodamine
B dyes, binds to early aggregates of the model protein cytoplasmic
glyceraldehyde-3-phosphate dehydrogenase 1 from Arabidopsis
thaliana (AtGAPC1) since the very onset of the oligomeric
phase, making them brightly fluorescent. This initial step of aggregation
has, until now, remained elusive with other fluorescence- or scattering-based
techniques. The information gathered from nanotracking (via light-sheet
fluorescence microscopy) and from FCS in a confocal microscope converges
to highlight the ability of HA-RB to bind protein aggregates from
the very early steps of aggregation and with high affinity. Altogether,
this fluorescence-based approach allows one to monitor and track individual
early AtGAPC1 aggregates in the size range from 10 to 100 nm with
high time (∼10–2 s) and space (∼250 nm) resolution.