Conserved loop of a phase modifier endows protein condensates with fluidity

Kawamukai, H.; Matsusaki, M.; Tanimoto, T.; Watabe, M.; Morishima, K.; Tomita, S.; Shinkai, Y.; Niwa, T.; Mannen, T.; Kumeta, H.; Nanaura, H.; Kato, K.; Mabuchi, T.; Aiba, Y.; Uehara, T.; Isozumi, N.; Hara, Y.; Kanemura, S.; Matsumura, H.; Sugie, K.; Ishimori, K.; Muraoka, T.; Sugiyama, M.; Okumura, M.; Mori, E.; Yoshizawa, T.; Saio, T.

doi:10.1101/2024.07.03.601791

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bioRxiv · 10.1101/2024.07.03.601791

Conserved loop of a phase modifier endows protein condensates with fluidity

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Abstract

Dipeptide repeats (DPRs) that are gene products from abnormal hexanucleotide repeat expansion in C9orf72 trigger amyotrophic lateral sclerosis (ALS) through unknown mechanism. This study highlights, importin Karyopherin{beta}2 (Kap{beta}2), which is responsible for nuclear transport and phase modification of RNA-binding proteins (RBPs), as a major DPR target. We demonstrate DPR accumulation in the nucleus via Kap{beta}2-mediated transport, which results in dose-dependent toxicity observed in nematode and yeast models. In vitro interaction studies exploiting chemical probe arrays and biophysical measurements reveal multivalent DPR binding to Kap{beta}2, including at the conserved acidic loop. Refractive index and fluorescence imaging coupled with biochemical assays unveiled that binding of excess DPRs to the acidic loop turns a phase modifier Kap{beta}2 into phase disrupter, resulting more condensed and viscous RBP condensates. Our findings provides molecular insight into C9orf72-ALS related to age and repeat expansion.

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Kawamukai, H., Matsusaki, M., Tanimoto, T., Watabe, M., Morishima, K., Tomita, S., Shinkai, Y., Niwa, T., Mannen, T., Kumeta, H., Nanaura, H., Kato, K., Mabuchi, T., Aiba, Y., Uehara, T., Isozumi, N., Hara, Y., Kanemura, S., Matsumura, H., Sugie, K., Ishimori, K., Muraoka, T., Sugiyama, M., Okumura, M., Mori, E., Yoshizawa, T., Saio, T.. 2024-07-04. Conserved loop of a phase modifier endows protein condensates with fluidity. https://doi.org/10.1101/2024.07.03.601791

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