  Intrinsically disordered proteins (IDPs) are a subset of proteins that lack
stable secondary structure. Given their polymeric nature, previous mean-field
approximations have been used to describe the statistical structure of IDPs.
However, the amino-acid sequence heterogeneity and complex intermolecular
interaction network have significantly impeded the ability to get proper
approximations. One such case is the intrinsically disordered tail domain of
Neurofilament low (NFLt), which comprises a 50 residue-long uncharged domain
followed by a 96 residue-long negatively charged domain. Here, we measure two
NFLt variants to identify the impact of the NFLt two main subdomains on its
complex interactions and statistical structure. Using synchrotron small-angle
x-ray scattering, we find that the uncharged domain of the NFLt induces
attractive interactions that cause it to self-assemble into star-like polymer
brushes. On the other hand, when the uncharged domain is truncated, the
remaining charged N-terminal domains remain isolated in solution with typical
polyelectrolyte characteristics. We further discuss how competing long- and
short-ranged interactions within the polymer brushes dominate their ensemble
structure, and, in turn, their implications on previously observed phenomena in
NFL native and diseased states.
