Multiple discrete soluble aggregates influence polyglutamine toxicity in a Huntington\u27s disease model system

Huntington’s disease (HD) results from expansions of polyglutamine stretches (polyQ) in the huntingtin protein (Htt) that promote protein aggregation, neurodegeneration, and death. Since the diversity and sizes of the soluble Htt-polyQ aggregates that have been linked to cytotoxicity are unknown, we investigated soluble Htt-polyQ aggregates using analytical ultracentrifugation. Soon after induction in a yeast HD model system, non-toxic Htt-25Q and cytotoxic Htt-103Q both formed soluble aggregates 29S to 200S in size. Because current models indicate that Htt-25Q does not form soluble aggregates, reevaluation of previous studies may be necessary. Only Htt-103Q aggregation behavior changed, however, with time. At 6 hr mid-sized aggregates (33S to 84S) and large aggregates (greater than 100S) became present while at 24 hr primarily only mid-sized aggregates (20S to 80S) existed. Multiple factors that decreased cytotoxicity of Htt-103Q (changing the length of or sequences adjacent to the polyQ, altering ploidy or chaperone dosage, or deleting anti-aging factors) altered the Htt-103Q aggregation pattern in which the suite of mid-sized aggregates at 6 hr were most correlative with cytotoxicity. Hence, the amelioration of HD and other neurodegenerative diseases may require increased attention to and discrimination of the dynamic alterations in soluble aggregation processes

Stoichiometry and Change of the mRNA Closed-Loop Factors as Translating Ribosomes Transit from Initiation to Elongation

Protein synthesis is a highly efficient process and is under exacting control. Yet, the actual abundance of translation factors present in translating complexes and how these abundances change during the transit of a ribosome across an mRNA remains unknown. Using analytical ultracentrifugation with fluorescent detection we have determined the stoichiometry of the closed-loop translation factors for translating ribosomes. A variety of pools of translating polysomes and monosomes were identified, each containing different abundances of the closed-loop factors eIF4E, eIF4G, and PAB1 and that of the translational repressor, SBP1. We establish that closed-loop factors eIF4E/eIF4G dissociated both as ribosomes transited polyadenylated mRNA from initiation to elongation and as translation changed from the polysomal to monosomal state prior to cessation of translation. eIF4G was found to particularly dissociate from polyadenylated mRNA as polysomes moved to the monosomal state, suggesting an active role for translational repressors in this process. Consistent with this suggestion, translating complexes generally did not simultaneously contain eIF4E/eIF4G and SBP1, implying mutual exclusivity in such complexes. For substantially deadenylated mRNA, however, a second type of closed-loop structure was identified that contained just eIF4E and eIF4G. More than one eIF4G molecule per polysome appeared to be present in these complexes, supporting the importance of eIF4G interactions with the mRNA independent of PAB1. These latter closed-loop structures, which were particularly stable in polysomes, may be playing specific roles in both normal and disease states for specific mRNA that are deadenylated and/or lacking PAB1. These analyses establish a dynamic snapshot of molecular abundance changes during ribosomal transit across an mRNA in what are likely to be critical targets of regulation

2-(5-Bromo­pent­yl)-4-chloro-5-[2-(4-meth­oxy­phen­yl)ethyl­amino]­pyridazin-3(2H)-one

The asymmetric unit of the title compound, C18H23BrClN3O2, consists of two mol­ecules which exhibit different conformations of the pentyl chains [C—C—C—C torsion angles of −60.4 (4) and 175.8 (3)°]. The crysal packing exhibits a chain structure, generated through the O atom of the pyridazinone forming a hydrogen bond with the N—H group of an adjacent mol­ecule

1-(2-Fluoro­benz­yl)quinolinium bis­(2-sulfanylidene-1,3-dithiole-4,5-dithiol­ato-κ2 S,S′)nickelate(III)

The crystal structure of the title compound, (C16H13FN)[Ni(C3S5)2], consists of NiIII complex anions and 1-(2-fluoro­benz­yl)quinolinium (fbq) cations. In the complex anion, the NiIII cation is chelated by two 2-sulfanylidene-1,3-dithiole-4,5-dithiol­ate (dmit) dianions in a distorted square-planar geometry; the two dmit mean planes are twisted with respect to each other at a dihedral angle of 8.44 (3)°. In the fbq cation, the dihedral angle between the benzene ring and the quinoline ring system is 80.57 (14)°. The centroid–centroid distance of 3.860 (5) Å between benzene rings indicates π–π stacking between adjacent fbq cations. The distance of 3.4958 (18) Å between the S atom and the centroid of the pyridine ring suggests the existence of a lone-pair–aromatic inter­action between the anion and the cation. A short S⋯S contact [3.387 (2) Å] is also observed in the crystal structure