Untangling aggregates one step at a time: Conserved AAA+ protein complexes exploit adenosine triphosphate hydrolysis to unfold and disaggregate their substrates in response to cell stress, but exactly how they do this has been unclear. Gates et al. determined high-resolution cryo-electron microscopy structures of the Hsp104 disaggregase bound to an unfolded polypeptide substrate in its channel. The structures reveal substrate interactions and two different translocation states. Hsp104 undergoes conformational changes that drive movement along the substrate by two-amino-acid steps. These states help explain how this molecular machine can solubilize protein aggregates and amyloids. Science , this issue p. 273

Cytoplasmic inclusions of the RNA-binding protein fused in sarcoma (FUS) represent one type of membraneless ribonucleoprotein compartment. Formation of FUS inclusions is promoted by amyotrophic lateral sclerosis (ALS)–linked mutations, but the cellular functions affected upon inclusion formation are poorly defined. In this study, we find that FUS inclusions lead to the mislocalization of specific RNAs from fibroblast cell protrusions and neuronal axons. This is mediated by recruitment of kinesin-1 mRNA and protein within FUS inclusions, leading to a loss of detyrosinated glutamate (Glu)–microtubules (MTs; Glu-MTs) and an inability to support the localization of RNAs at protrusions. Importantly, dissolution of FUS inclusions using engineered Hsp104 disaggregases, or overexpression of kinesin-1, reverses these effects. We further provide evidence that kinesin-1 affects MT detyrosination not through changes in MT stability, but rather through targeting the tubulin carboxypeptidase enzyme onto specific MTs. Interestingly, other pathological inclusions lead to similar outcomes, but through apparently distinct mechanisms. These results reveal a novel kinesin-dependent mechanism controlling the MT cytoskeleton and identify loss of Glu-MTs and RNA mislocalization as common outcomes of ALS pathogenic mutations.