6 research outputs found
Recent developments in designing optical sensors for detection of basic amino acids
293-300In recent times, amino acids have been discovered as key mediators in regulating human health, metabolism, and nutrition, which has prompted an active research in developing sensor systems that offer a simple and rapid detection of amino acids. In this review article, our goal is to discuss the recent developments in designing fluorimetric and colorimetric sensors, in particular, for detection of basic amino acids. We have divided the existing contributions based on either different materials or a different class of fluorophores. Moreover, we have briefly highlighted recently devised ratiometric sensors for detection of basic amino acids. Through this review article, we aim to provide the readers a comprehensive overview of the developments in the optical sensing of basic amino acids
Supramolecular Dye Aggregate Assembly Enables Ratiometric Detection and Discrimination of Lysine and Arginine in Aqueous Solution
Constructing
sensor systems for rapid and selective detection of
small biomolecules such as amino acids is a major area of focus in
bioanalytical chemistry. Considering the biological relevance of arginine
and lysine, significant efforts have been directed to develop fluorescent
sensors for their detection. However, these developed sensors suffer
from certain disadvantages such as poor aqueous solubility, technically
demanding and time-consuming synthetic protocols, and more importantly,
most of them operate through single wavelength measurements, making
their performance prone to small variations in experimental conditions.
Herein, we report a ratiometric sensor that operates through lysine-
and arginine-induced dissociation of a supramolecular assembly consisting
of emissive H-aggregates of a molecular rotor dye, thioflavin-T (ThT),
on the surface of a polyanionic supramolecular host, sulfated β-cyclodextrin.
This disassembly brings out the modulation of monomer–aggregate
equilibrium in the system which acts as an ideal scheme for the ratiometric
detection of lysine and arginine in the aqueous solution. Besides
facile framework of our sensor system, it employs a commercially available
inexpensive probe molecule, ThT, which provides an added advantage
over other sensor systems that employ synthetically demanding probe
molecules. Importantly, the distinctive feature of the ratiometric
detection of arginine and lysine provides an inherent advantage of
increased accuracy in quantitative analysis. Interestingly, we have
also demonstrated that arginine displays a multiwavelength distinctive
recognition pattern which distinguishes it from lysine, using a single
supramolecular ensemble. Furthermore, our sensor system also shows
response in heterogeneous, biologically complex media of serum samples,
thus extending its possible use in real-life applications
Evaluation of an Ultrafast Molecular Rotor, Auramine O, as a Fluorescent Amyloid Marker
Recently,
Auramine O (AuO) has been projected as a fluorescent
fibril sensor, and it has been claimed that AuO has an advantage over
the most extensively utilized fibril marker, Thioflavin-T (ThT), owing
to the presence of an additional large red-shifted emission band for
AuO, which was observed exclusively for AuO in the presence of fibrillar
media and not in protein or buffer media. As fibrils are very rich
in β-sheet structure, a fibril sensor should be more specific
toward the β-sheet structure so as to produce a large contrast
between the fibril form and native protein form, for efficient detection
and in vitro mechanistic studies of fibrillation. However, in this
report, we show that AuO interacts significantly with the native form
of bovine serum albumin (BSA), which is an all-α-helical protein
and lacks the β-sheet structure, which are the hallmarks of
a fibrillar structure. This strong interaction of AuO with the native
form of BSA leads to a large emission enhancement of AuO for the native
protein itself, and leads to a low contrast between the BSA protein
and its fibrils. More importantly, the large red-shifted emission
band of AuO, reported in the presence of human insulin fibrils, and
which was projected as its major advantage over ThT, is not observed
in the presence of BSA fibrils as well as fibrils from other proteins,
such as lysozyme, human serum albumin, and β-lactoglobulin.
Thus, our results provide information on the
universal applicability of the distinctive and claimed-to-be-advantageous
photophysical features reported for AuO in human insulin fibrils towards
fibrils from other proteins. Time-resolved fluorescence measurements
also support the proposition of a strong interaction of AuO with native
BSA. Additionally, tryptophan emission of the protein has been explored
to further elucidate the binding mechanism of AuO with native BSA.
Evaluation of thermodynamic parameters revealed that the binding of
AuO with native BSA involved positive enthalpy and entropy changes,
suggesting dominant contributions from hydrophobic and electrostatic
interactions toward the association of AuO with native BSA. Molecular
docking calculations have been performed to identify the principal
binding location of AuO in native BSA
On the Molecular Form of Amyloid Marker, Auramine O, in Human Insulin Fibrils
Designing extrinsic fluorescence
sensors for amyloid fibrils is
a very active and important area of research. Recently, an ultrafast
molecule rotor dye, Auramine O (AuO), has been projected as a fluorescent
amyloid marker. It has been claimed that AuO scores better than the
most extensively utilized gold-standard amyloid probe, Thioflavin-T
(ThT). This advantage arises from the fact that AuO, in addition to
its usual emission band (∼500 nm), also displays a large red-shifted
emission band (∼560 nm), exclusively in the presence of human
insulin fibril medium
and not in the native protein or buffer media. On the contrary, for
ThT, the emission maximum (∼490 nm) largely remains unchanged
while going from protein to fibril. This otherwise unknown large red-shifted
emission band of AuO, observed in the presence of human insulin fibrils,
was tentatively attributed to a species formed upon fast proton dissociation
from excited AuO. It was proposed that because of the long excited-state
lifetime (∼1.8 ns) of AuO upon association with human insulin
fibrils, this fast proton dissociation from excited AuO could be observed,
which is otherwise not observed in buffer or native protein media,
owing to its very short excited-state lifetime (∼1 ps). Herein,
we show that despite the long excited-state lifetime of AuO in other
fibrillar media (human serum albumin and lysozyme), the new red-shifted
emission band at 560 nm is not observed, thus possibly suggesting
a different origin of the red-shifted emission band of AuO in human
insulin fibril medium. We convincingly show that this red-shifted
band of AuO (∼560 nm) could be observed under conditions that
promote dye aggregation, such as a premicellar concentration of surfactants
and polyelectrolytes. These AuO aggregates display strong emission
wavelength dependence of transient decay traces, similar to that for
AuO in human insulin fibril medium. Detailed time-resolved emission
spectral (TRES) measurements suggest that the AuO/premicellar surfactant
and AuO/human insulin fibril system share similar features, such as
a dynamic red-shift in TRES and an isoemissive point in the time-resolved
area-normalized emission spectra, suggesting that the characteristic
red-shifted emission band of AuO in human insulin fibril medium may
arise from AuO aggregates
Aspirin Inhibition of Group VI Phospholipase A2 Induces Synthetic Lethality in AAM Pathway Down-Regulated Gingivobuccal Squamous Carcinoma
Background: To elucidate the role of iPLA2/PLA2G6 in gingivobuccal squamous cell carcinoma (GB-SCC) and to ascertain the synthetic lethality-based chemoprevention role of aspirin in arachidonic acid metabolism (AAM) pathway down-regulated GB-SCC. Methods: The in vitro efficacy of aspirin on GB-SCC cells (ITOC-03 and ITOC-04) was assessed by cell proliferation, colony formation, apoptosis, cell migration, cell cycle assay and RNA-seq, while inhibition of PLA2G6 and AAM pathway components was affirmed by qPCR, Western blot and immunofluorescence staining. The in vivo effect of aspirin was evaluated using NOD-SCID mice xenografts and immunohistochemical analysis. Results: We found that aspirin, which has been reported to act through the COX pathway, is inhibiting PLA2G6, and thereby the COX and LOX components of the AAM pathway. The findings were validated using PLA2G6 siRNA and immunohistochemical marker panel. Moreover, a pronounced effect in ITOC-04 cells and xenografts implied aspirin-induced synthetic lethality in the AAM pathway down-regulated GB-SCC. Conclusions: This study reveals that aspirin induces the anti-tumor effect by a previously unrecognized mechanism of PLA2G6 inhibition. In addition, the effect of aspirin is influenced by the baseline AAM pathway status and could guide precision prevention clinical trials of AAM pathway inhibitors