Ghrelin proteolysis by insulin-degrading enzyme

Here we report proteolysis of synthetic acylated human ghrelin by recombinant human insulin-degrading enzyme (IDE). Kinetic parameters and sites of proteolytic cleavage were evaluated. Ghrelin proteolysis by IDE was inhibited by ethylenediaminetetraacetate (EDTA), a metal chelating agent. Ghrelin proteolysis appears at least somewhat specific to M16 family proteases such as IDE, as the M13 protease neprilysin (NEP) did not exhibit ghrelin proteolysis in this study. A quenched fluorogenic peptide substrate comprising the primary sites of IDE-mediated ghrelin proteolysis (Mca-QRVQQRKESKK(Dnp)-OH; Mca: 7-methoxycoumarin-3-carboxylic acid; Dnp: 2,4-dinitrophenyl) was developed and used to evaluate enzyme specificity and kinetic parameters of proteolysis. Like acyl ghrelin, Mca-QRVQQRKESKK(Dnp)-OH was efficiently cleaved by IDE central to the target sequence. We anticipate that this quenched fluorogenic peptide substrate will be of value to future studies of ghrelin proteolysis by IDE and potentially other peptidases.

Multifunctional Thio-Stabilized Gold Nanoparticles for Near-Infrared Fluorescence Detection and Imaging of Activated Caspase-3

Background: Gold nanoparticles (AuNPs) are commonly used in nanomedicine because of their unique spectral properties, chemical and biological stability, and ability to quench the fluorescence of organic dyes attached to their surfaces. However, the utility of spherical AuNPs for activatable fluorescence sensing of molecular processes have been confined to resonance-matched fluorophores in the 500 nm to 600 nm spectral range to maximize dye fluorescence quenching efficiency. Expanding the repertoire of fluorophore systems into the NIR fluorescence regimen with emission >800 nm will facilitate the analysis of multiple biological events with high detection sensitivity. Objective: The primary goal of this study is to determine if spherical AuNP-induced radiative rate suppression of nonresonant near-infrared (NIR) fluorescent probes can serve as a versatile nanoconstruct for highly sensitive detection and imaging of activated caspase-3 in aqueous media and cancer cells. This required the development of activatable NIR fluorescence sensors of caspase-3 designed to overcome the nonspecific degradation and release of the surface coatings in aqueous media. Method: We harnessed the fluorescence-quenching properties and multivalency of spherical AuNPs to develop AuNPtemplated activatable NIR fluorescent probes to detect activated caspase-3, an intracellular reporter of early cell death. Freshly AuNPs were coated with a multifunctional NIR fluorescent dye-labeled peptide (LS422) consisting of an RGD peptide sequence that targets αvβ3-integrin protein (αvβ3) on the surface of cancer cells to mediate the uptake and internalization of the sensors in tumor cells; a DEVD peptide sequence for reporting the induction of cell death through caspase-3 mediated NIR fluorescence enhancement; and a multidentate hexacysteine sequence for enhancing selfassembly and stabilizing the multifunctional construct on AuNPs. The integrin binding affinity of LS422 and caspase-3 kinetics were determined by a radioligand competitive binding and fluorogenic peptide assays, respectively. Detection of intracellular caspase-3, cell viability, and the internalization of LS422 in cancer cells were determined by confocal NIR fluorescence spectroscopy and microscopy. Results: Narrow size AuNPs (13 nm) were prepared and characterized by transmission electron microscopy and dynamic light scattering. When assembled on the AuNPs, the binding constant of LS422 for αvβ3 improved 11-fold from 13.2 nM to 1.2 nM. Whereas the catalytic turnover of caspase-3 by LS422-AuNPs was similar to the reference fluorogenic peptide, the binding affinity for the enzyme increased by a factor of 2. Unlike the αvβ3 positive, but caspase-3 negative breast cancer MCF-7 cells, treatment of the αvβ3 and caspase-3 positive lung cancer A549 cells with Paclitaxel showed significant fluorescence enhancement within 30 minutes, which correlated with caspase-3 specific activation of LS422- AuNPs fluorescence. Incorporation of a 3.5 mW NIR laser source into our spectrofluorometer increased the detection sensitivity by an order of magnitude (limit of detection ~0.1 nM of cypate) and significantly decreased the signal noise relative to a xenon lamp. This gain in sensitivity enabled the detection of substrate hydrolysis at a broad range of inhibitor concentrations without photobleaching the cypate dye. Conclusion: The multifunctional AuNPs demonstrate the use of a non-resonant quenching strategy to design activatable NIR fluorescence molecular probes. The nanoconstruct offers a selective reporting method for detecting activated caspase-3, imaging of cell viability, identifying dying cells, and visualizing the functional status of intracellular enzymes. Performing these tasks with NIR fluorescent probes creates an opportunity to translate the in vitro and cellular analysis of enzymes into in vivo interrogation of their functional status using deep tissue penetrating NIR fluorescence analytical methods.

A fluorogenic peptide-based smartprobe for the detection of neutrophil extracellular traps and inflammation

A highly specific, fluorogenic probe detects human neutrophil elastase (hNE) in activated neutrophils and Neutrophil Extracellular Traps (NETs).

Supramolecular fluorogenic peptide sensor array based on graphene oxide for the differential sensing of ebola virus

Principal component analysis of a fluorescent supramolecular sensor array based on graphene oxide can be used to differentiate ebola virus from marburg virus and receptor-extensive vesicular stomatitis virus.

Instantaneous detection of αs-casein in cow's milk using fluorogenic peptide aptamers

We present a novel, fluorogenic peptide aptamer that strongly enhances its fluorescence just after mixing it with a milk allergen αs-casein. Notably, our system can detect αs-casein in an exceptionally short time of 20–25 seconds.

Development of Chemical Tools to Monitor Human Kallikrein 13 (KLK13) Activity

Kallikrein 13 (KLK13) was first identified as an enzyme that is downregulated in a subset of breast tumors. This serine protease has since been implicated in a number of pathological processes including ovarian, lung and gastric cancers. Here we report the design, synthesis and deconvolution of libraries of internally quenched fluorogenic peptide substrates to determine the specificity of substrate binding subsites of KLK13 in prime and non-prime regions (according to the Schechter and Berger convention). The substrate with the consensus sequential motive ABZ-Val-Arg-Phe-Arg-ANB-NH2 demonstrated selectivity towards KLK13 and was successfully converted into an activity-based probe by the incorporation of a chloromethylketone warhead and biotin bait. The compounds described may serve as suitable tools to detect KLK13 activity in diverse biological samples, as exemplified by overexpression experiments and targeted labeling of KLK13 in cell lysates and saliva. In addition, we describe the development of selective activity-based probes targeting KLK13, to our knowledge the first tool to analyze the presence of the active enzyme in biological samples.