R ataxin-3(Q15) and the Josephin domain (Fig. S1).SDS-insoluble Aggregation of Pathogenic Length Ataxin3 is Affected by SDSHaving demonstrated that the effects of SDS on the formation of SDS-soluble stage 1 fibrils are similar to those previously reported for other amyloid proteins, we then investigated the effects of SDS on the second stage of the multi-stage ataxin-3 aggregation pathway. The formation of stage 2 aggregates can be monitored using a membrane filter trap assay in which after boiling in 2 (w/v) SDS, only SDS-insoluble fibrils are retained upon the filter. It should be noted that the concentration of SDS used to solubilize the fibrils (2 (w/v) SDS) is six times greater than the concentrations around the CMC which impact upon fibrillogenesis (0.03 ?.29 ). It can clearly be seen that in the absence of SDS ataxin-3(Q64) forms SDS-insoluble aggregates following 51 hrs of incubation (Fig. 3A). With 0?0 mM SDS, both non-pathogenic length ataxin-3(Q15) and the Josephin domain did not form SDS-insoluble aggregates when incubated up to 200 hours (data not shown). Although it was anticipated that due to the sequential nature of the aggregation pathway modulation of stage 1 aggregation would mediate similar kinetic effects on stage 2 aggregation [45], quite different results were obtained. Despite 1 mM SDS significantly accelerating the rate of SDS-soluble fibril formation as detected by thioT fluorescence (Fig. 2A), the formation of SDS-insoluble fibrils by ataxin-3(Q64) with 1 mM SDS is slower and has a midpoint 24 hours later than in the absence of SDS (Fig. 3A,B; Table 2). In contrast, ataxin-3(Q64) with 5 mM SDS shows no increase in thioT fluorescence over 100 hours (Fig. 2A) yet the formation of SDS-insoluble aggregates appear in the filter trap assay from 51 hours (Fig. 3A,B), suggesting that the aggregates are forming on an alternative aggregation pathway. Addition of the polyQ-binding peptide QBP1 eliminated the formation of SDS-insoluble aggregates formed by ataxin-3(Q64) with 5 mM SDS. In a strongly micellar environment (10 mM SDS), ataxin3(Q64) does not show the formation of MedChemExpress Dimethylenastron either SDS-soluble (Fig. 2A) or SDS-insoluble aggregates (Fig. 3A,B). Several studies have reported distinct effects of micellar and Lixisenatide non-micellar SDS concentrations, with micellar concentrations inhibiting aggregation, and non-micellar concentrations accelerating aggregation [37?9]. However with the complexity of the two-stage ataxin-3 aggregation mechanism, there is 23727046 not such a clear distinction. Only the highly micellar 10 mM SDS inhibits both stages of the pathway, and the other SDS concentrations differentially affect the first and second stages of aggregation.SDS Addition Results in Changed Morphology of FibrilsThe formation of SDS insoluble fibrils which are not thioT reactive suggests that ataxin-3 is forming these fibrils via an atypical pathway. In order to investigate this further, TEM was used to visualize the morphology of the aggregates being formed with 0, 1, 5 and 10 mM SDS present (Fig. 5, Fig. S2). As expected, ataxin-3(Q64) in the presence of 10 mM SDS did not form fibrils (data not shown). In contrast, with 23977191 5 mM SDS ataxin-3(Q64) forms amorphous aggregates with a diameter of 20?0 nm which although SDS-insoluble, do not have a fibrillar morphology but appear clumped together to form large amorphous aggregates of up to 0.5 mm in length (Fig. 5C and F). The fibrils formed by ataxin-3(Q64) in the presence of 1 mM SDS (Fig. 5B) had leng.R ataxin-3(Q15) and the Josephin domain (Fig. S1).SDS-insoluble Aggregation of Pathogenic Length Ataxin3 is Affected by SDSHaving demonstrated that the effects of SDS on the formation of SDS-soluble stage 1 fibrils are similar to those previously reported for other amyloid proteins, we then investigated the effects of SDS on the second stage of the multi-stage ataxin-3 aggregation pathway. The formation of stage 2 aggregates can be monitored using a membrane filter trap assay in which after boiling in 2 (w/v) SDS, only SDS-insoluble fibrils are retained upon the filter. It should be noted that the concentration of SDS used to solubilize the fibrils (2 (w/v) SDS) is six times greater than the concentrations around the CMC which impact upon fibrillogenesis (0.03 ?.29 ). It can clearly be seen that in the absence of SDS ataxin-3(Q64) forms SDS-insoluble aggregates following 51 hrs of incubation (Fig. 3A). With 0?0 mM SDS, both non-pathogenic length ataxin-3(Q15) and the Josephin domain did not form SDS-insoluble aggregates when incubated up to 200 hours (data not shown). Although it was anticipated that due to the sequential nature of the aggregation pathway modulation of stage 1 aggregation would mediate similar kinetic effects on stage 2 aggregation [45], quite different results were obtained. Despite 1 mM SDS significantly accelerating the rate of SDS-soluble fibril formation as detected by thioT fluorescence (Fig. 2A), the formation of SDS-insoluble fibrils by ataxin-3(Q64) with 1 mM SDS is slower and has a midpoint 24 hours later than in the absence of SDS (Fig. 3A,B; Table 2). In contrast, ataxin-3(Q64) with 5 mM SDS shows no increase in thioT fluorescence over 100 hours (Fig. 2A) yet the formation of SDS-insoluble aggregates appear in the filter trap assay from 51 hours (Fig. 3A,B), suggesting that the aggregates are forming on an alternative aggregation pathway. Addition of the polyQ-binding peptide QBP1 eliminated the formation of SDS-insoluble aggregates formed by ataxin-3(Q64) with 5 mM SDS. In a strongly micellar environment (10 mM SDS), ataxin3(Q64) does not show the formation of either SDS-soluble (Fig. 2A) or SDS-insoluble aggregates (Fig. 3A,B). Several studies have reported distinct effects of micellar and non-micellar SDS concentrations, with micellar concentrations inhibiting aggregation, and non-micellar concentrations accelerating aggregation [37?9]. However with the complexity of the two-stage ataxin-3 aggregation mechanism, there is 23727046 not such a clear distinction. Only the highly micellar 10 mM SDS inhibits both stages of the pathway, and the other SDS concentrations differentially affect the first and second stages of aggregation.SDS Addition Results in Changed Morphology of FibrilsThe formation of SDS insoluble fibrils which are not thioT reactive suggests that ataxin-3 is forming these fibrils via an atypical pathway. In order to investigate this further, TEM was used to visualize the morphology of the aggregates being formed with 0, 1, 5 and 10 mM SDS present (Fig. 5, Fig. S2). As expected, ataxin-3(Q64) in the presence of 10 mM SDS did not form fibrils (data not shown). In contrast, with 23977191 5 mM SDS ataxin-3(Q64) forms amorphous aggregates with a diameter of 20?0 nm which although SDS-insoluble, do not have a fibrillar morphology but appear clumped together to form large amorphous aggregates of up to 0.5 mm in length (Fig. 5C and F). The fibrils formed by ataxin-3(Q64) in the presence of 1 mM SDS (Fig. 5B) had leng.
