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.
We report the serendipitous discovery of an optical mercury sensor while trying to develop a water-soluble manganese probe. The sensor is based on a pentaaza macrocycle conjugated to a hemicyanine dye. The pentaaza macrocycle earlier designed in our group was used to develop photoinduced electron transfer (PET)-based "turn-on" fluorescent sensors for manganese. (1) In an attempt to increase the water-solubility of the manganese sensors we changed the dye from BODIPY to hemicyanine. The resultant molecule qHCM afforded a distinct reversible change in the absorption features and a concomitant visible color change upon binding to Hg ions, leading to a highly water-soluble mercury sensor with a 10 ppb detection limit. The molecule acts as a reversible "ON-OFF" fluorescent sensor for Hg with a 35 times decrease in the emission intensity in the presence of 1 equiv of Hg ions. We have demonstrated the applicability of the probe for detecting Hg ions in living cells and in live zebrafish larvae using confocal fluorescence microscopy with visible excitation. High selectivity and sensitivity toward Hg detection make qHCM an attractive probe for detecting Hg in contaminated water sources, which is a major environmental toxicity concern. We have scrutinized the altered metal-ion selectivity of the probe using density functional theory (DFT) and time-dependent DFT calculations, which show that a PET-based metal-sensing scheme is not operational in qHCM. H NMR studies and DFT calculations indicate that Hg ions coordinate to oxygen-donor atoms from both the chromophore and macrocycle, leading to sensitive mercury detection.
Several substrates containing both cyano and Weinreb amide functionalities have been synthesized to study the chemoselectivity of their reactions with organomagnesium bromides (ArMgBr and RMgBr). Excellent chemoselectivity towards the Weinreb amide was observed in most cases, even in the presence of excess Grignard reagent, affording cyano ketones in good‐to‐excellent yields.
Phosphoinositides are critical cell-signal mediators present on the plasma membrane. The dynamic change of phosphoinositide concentrations on the membrane including clustering and declustering mediates signal transduction. The importance of phosphoinositides is scored by the fact that they participate in almost all cell-signaling events, and a defect in phosphoinositide metabolism is linked to multiple diseases including cancer, bipolar disorder, and type-2 diabetes. Optical sensors for visualizing phosphoinositide distribution can provide information on phosphoinositide dynamics. This exercise will ultimately afford a handle into understanding and manipulating cell-signaling processes. The major requirement in phosphoinositide sensor development is a selective, cell permeable probe that can quantify phosphoinositides. To address this requirement, we have developed short peptide-based ratiometric fluorescent sensors for imaging phosphoinositides. The sensors afford a selective response toward two crucial signaling phosphoinositides, phosphatidylinositol-4,5-bisphosphate (PI(4,5)P2) and phosphatidylinositol-4-phosphate (PI4P), over other anionic membrane phospholipids and soluble inositol phosphates. Dissociation constant values indicate up to 4 times higher probe affinity toward PI(4,5)P2 when compared to PI4P. Significantly, the sensors are readily cell-permeable and enter cells within 15 min of incubation as indicated by multiphoton excitation confocal microscopy. Furthermore, the sensors light up signaling phosphoinositides present both on the cell membrane and on organelle membranes near the perinuclear space, opening avenues for quantifying and monitoring phosphoinositide signaling.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.