A minimal construct of nuclear-import receptor Karyopherin-β2 defines the regions critical for chaperone and disaggregation activity

Karyopherin-P2 (KapP2) is a nuclear-import receptor that recognizes proline-tyrosine nuclear localization signals of diverse cytoplasmic cargo for transport to the nucleus. KapP2 cargo includes several disease-linked RNA-binding proteins with prion-like domains, such as FUS, TAF15, EWSR1, hnRNPA1, and hnRNPA2. These RNA-binding proteins with prion-like domains are linked via pathology and genetics to debilitating degenerative disorders, including amyotrophic lateral sclerosis, frontotemporal dementia, and multisystem proteinopathy. Remarkably, KapP2 prevents and reverses aberrant phase transitions of these cargoes, which is cytopro-tective. However, the molecular determinants of KapP2 that enable these activities remain poorly understood, particularly from the standpoint of nuclear-import receptor architecture. KapP2 is a super-helical protein comprised of 20 HEAT re-peats. Here, we design truncated variants of KapP2 and assess their ability to antagonize FUS aggregation and toxicity in yeast and FUS condensation at the pure protein level and in human cells. We find that HEAT repeats 8 to 20 of KapP2 recapitulate all salient features of KapP2 activity. By contrast, KapP2 trun-cations lacking even a single cargo-binding HEAT repeat display reduced activity. Thus, we define a minimal KapP2 construct for delivery in adeno-associated viruses as a potential therapeutic for amyotrophic lateral sclerosis/frontotemporal dementia, multisystem proteinopathy, and related disorders.

Automated summary

KapP2 is a nuclear-import receptor that transports various cytoplasmic cargo, including disease-linked RNA-binding proteins, to the nucleus. These RNA-binding proteins with prion-like domains are associated with degenerative disorders. KapP2 can prevent and reverse aberrant phase transitions of these proteins, providing cytoprotection. The molecular determinants of KapP2's activities are poorly understood, but truncations lacking cargo-binding repeats show reduced activity. HEAT repeats 8 to 20 of KapP2 recapitulate its activity, making them a potential therapeutic target for related disorders.