We tune the coordination environment of macrocyclic ligands to design two novel fluorescence sensors for Mn(2+). The BODIPY-based Mn(2+) sensor M1 affords an excellent, 52 fold, fluorescence 'turn-on' response despite the paramagnetic nature of Mn(2+). The lipophilic probe is cell-permeable and confocal imaging demonstrates that the sensor distinctly detects Mn(2+) within live cells.
O-GlcNAc modification of the microtubule associated
protein tau and α-synuclein can directly inhibit the formation
of the associated amyloid fibers associated with major classes of
neurodegenerative diseases. However, the mechanism(s) by which this
posttranslational modification (PTM) inhibit amyloid aggregation are
still murky. One hypothesis is that O-GlcNAc simply
acts as a polyhydroxylated steric impediment to the formation of amyloid
oligomers and fibers. Here, we begin to test this hypothesis by comparing
the effects of O-GlcNAc to other similar monosaccharidesglucose, N-acetyl-galactosamine (GalNAc), or mannoseon α-synuclein
amyloid formation. Interestingly, we find that this quite reasonable
hypothesis is not entirely correct. More specifically, we used four
types of biochemical and biophysical assays to discover that the different
sugars display different effects on the inhibition of amyloid formation,
despite only small differences between the structures of the monosaccharides.
These results further support a more detailed investigation into the
mechanism of amyloid inhibition by O-GlcNAc and has
potential implications for the evolution of N-acetyl-glucosamine
as the monosaccharide of choice for widespread intracellular glycosylation.
Toxic amyloid aggregates are a feature of many neurodegenerative
diseases. A number of biochemical and structural studies have demonstrated
that not all amyloids of a given protein are equivalent but rather
that an aggregating protein can form different amyloid structures
or polymorphisms. Different polymorphisms can also induce different
amounts of pathology and toxicity in cells and in mice, suggesting
that the structural differences may play important roles in disease.
However, the features that cause the formation of polymorphisms in vivo are still being uncovered. Posttranslational modifications
on several amyloid forming proteins, including the Parkinson’s
disease causing protein α-synuclein, may be one such cause.
Here, we explore whether ubiquitination can induce structural changes
in α-synuclein aggregates in vitro. We used
protein chemistry to first synthesize ubiquitinated analogues at three
different positions using disulfide linkages. After aggregation, these
linkages can be reversed, allowing us to make relative comparisons
between the structures using a proteinase K assay. We find that, while
ubiquitination at residue 6, 23, or 96 inhibits α-synuclein
aggregation, only modification at residue 96 causes an alteration
in the aggregate structure, providing further evidence that posttranslational
modifications may be an important feature in amyloid polymorphism
formation.
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