Tawani, A.; Qian, S.; Sparks, S. E.; Sashi, P.; Cahill, S.; Rout, M.; Cowburn, D.

We describe an unprecedented SANS/solvent matched experiment with the aim of providing a meso-scale dynamic structural description of fuzzy complexes such as those formed by nuclear transport factors as they ferry cargo across the nuclear pore complex, whose description is normally limited by the large number of states and rapid time scales of interconversion. These contain repeat short linear interaction domains which are common features of many intrinsically disordered functional proteins - e.g., transcriptional regulators, and RNA-interaction domains associated with liquid-liquid phase separated non-membranous organelles. The novel approach uses site-specific deuteration, SANS, and model fitting to provide changes to average spatial distributions between interacting domains of FG Nups upon binding to the nuclear transport factor NTF2. The results support the fully disordered nature of phenylalanyl-glycyl repeats within FG Nups in their interactions with the nuclear transport factor in vitro, as well as the absence of significant inter-aromatic contacts, or of interchain linkage in complexes.