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Structure. 2019 Jun 4;27(6):937-951.e5. doi: 10.1016/j.str.2019.03.012. Epub 2019 Apr 11.

ALS-Linked Mutations Affect UBQLN2 Oligomerization and Phase Separation in a Position- and Amino Acid-Dependent Manner.

Author information

1
Departments of Biology and Chemistry, Syracuse University, Syracuse, NY 13244, USA.
2
Department of Chemistry, Syracuse University, Syracuse, NY 13244, USA.
3
Department of Biochemistry and Molecular Biology, SUNY Upstate Medical University, Syracuse, NY 13210, USA.
4
Department of Cell and Developmental Biology, SUNY Upstate Medical University, Syracuse, NY 13210, USA; Department of Biology, Syracuse University, Syracuse, NY 13244, USA.
5
Department of Biology, Syracuse University, Syracuse, NY 13244, USA.
6
Departments of Biology and Chemistry, Syracuse University, Syracuse, NY 13244, USA; Interdisciplinary Neuroscience Program, Syracuse University, Syracuse, NY 13244, USA. Electronic address: cacastan@syr.edu.

Abstract

Proteasomal shuttle factor UBQLN2 is recruited to stress granules and undergoes liquid-liquid phase separation (LLPS) into protein-containing droplets. Mutations to UBQLN2 have recently been shown to cause dominant X-linked inheritance of amyotrophic lateral sclerosis (ALS) and ALS/dementia. Interestingly, most of these UBQLN2 mutations reside in its proline-rich (Pxx) region, an important modulator of LLPS. Here, we demonstrated that ALS-linked Pxx mutations differentially affect UBQLN2 LLPS, depending on both amino acid substitution and sequence position. Using size-exclusion chromatography, analytical ultracentrifugation, microscopy, and NMR spectroscopy, we determined that those Pxx mutants that enhanced UBQLN2 oligomerization decreased saturation concentrations needed for LLPS and promoted solid-like and viscoelastic morphological changes to UBQLN2 liquid assemblies. Ubiquitin disassembled all LLPS-induced mutant UBQLN2 aggregates. We postulate that the changes in physical properties caused by ALS-linked Pxx mutations modify UBQLN2 behavior in vivo, possibly contributing to aberrant stress granule morphology and dynamics, leading to formation of inclusions, pathological characteristics of ALS.

KEYWORDS:

ALS; aggregation; liquid-liquid phase separation; oligomerization; proline-rich; protein quality control; self-assembly; ubiquilin-2; ubiquitin; viscoelasticity

PMID:
30982635
PMCID:
PMC6551275
[Available on 2020-06-04]
DOI:
10.1016/j.str.2019.03.012

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