A novel Cu(II)-assisted peptide fluorescent probe for highly sensitive detection of glyphosate in real samples: real application in test strips and smartphone

Glyphosate (Glyp) is an organophosphorus herbicide, and its abuse causes potential harm to the environment and human health. Thus, the development of simple and portable methods for rapid and visual detection of glyphosate is of great importance. Herein, we successfully developed a new fluorescent probe L with dansyl fluorophore as a fluorescent dye and tetrapeptide (Ala-Ser-Arg-His-NH2) as a recognition group. According to the design, L exhibited a specific fluorescence quenching response to Cu2+ and formed an L-Cu2+ ensemble with a molecular ratio of 2:1, demonstrating a limit of detection (LOD) as low as 12.04 nM. Interestingly, the L-Cu2+ ensemble as a relay response probe exhibited a specific fluorescence "off-on" response to glyphosate without interference from other pesticides and anions based on the strong complexation of glyphosate and Cu2+. The LOD of the L-Cu2+ ensemble for glyphosate was calculated as 12.59 nM. Additionally, the results of three recovery experiments with real samples showed that L has good practicability and accuracy in detecting glyphosate. Test strips were also fabricated to achieve facile detection of glyphosate to demonstrate the practical application potential of the L-Cu2+ ensemble. The L-Cu2+ ensemble was integrated with a smartphone for semi-quantification of glyphosate in a field environment under a 365 nm UV lamp.

Rational design of an N-terminal cysteine-containing tetrapeptide that inhibits tyrosinase and evaluation of its mechanism of action

There has been a resurgence of interest in bioactive peptides as therapeutic agents. This is particularly interesting for tyrosinase, which can be inhibited by thiol-containing peptides. This work demonstrates that an N-terminal cysteine-containing tetrapeptide can be rationally designed to inhibit tyrosinase activity in vitro and in cells. The tetrapeptide cysteine (C), arginine (R), asparagine (N) and leucine (L) or CRNL is a potent inhibitor of tyrosinase activity with an IC50 value of 39.62 ± 6.21 μM, which is comparable to currently used tyrosinase inhibitors. Through structure-activity studies and computational modeling, we demonstrate the peptide interacts with the enzyme via electrostatic (R with E322), hydrogen bonding (N with N260) and hydrophobic (L with V248) intermolecular interactions and that a combination of these is required for potent activity. Moreover, copper chelating activity might be one of the mechanisms of tyrosinase inhibition by CRNL. Kinetic studies show that tetrapeptide is a competitive inhibitor with two-step irreversible inhibition. In addition, CRNL had no toxicity and could reduce melanin levels in the murine melanoma cell line (B16F1). Overall, CRNL is a very promising candidate for hyperpigmentation treatment.

Investigation of the structure-activity relationship at the N-terminal part of minigastrin analogs

BACKGROUND

Over the last years, several strategies have been reported to improve the metabolic stability of minigastrin analogs. However, currently applied compounds still reveal limited in vitro and in vivo stability. We thus performed a glycine scan at the N-terminus of DOTA-MGS5 (DOTA-D-Glu-Ala-Tyr-Gly-Trp-(N-Me)Nle-Asp-1-Nal) to systematically analyze the peptide structure. We substituted N-terminal amino acids by simple PEG spacers and investigated in vitro stability in human serum. Furthermore, we evaluated different modifications on its tetrapeptide binding sequence (H-Trp-(N-Me)Nle-Asp-1-Nal-NH₂).

RESULTS

Affinity data of all glycine scan peptides were found to be in a low nanomolar range (4.2-8.5 nM). However, a truncated compound lacking the D-γ-Glu-Ala-Tyr sequence revealed a significant loss in CCK-2R affinity. Substitution of the D-γ-Glu-Ala-Tyr-Gly sequence of DOTA-γ-MGS5 (DOTA- D-γ-Glu-Ala-Tyr-Gly-Trp-(N-Me)Nle-Asp-1-Nal-NH₂) by polyethylene glycol (PEG) spacers of different length exhibited only a minor influence on CCK-2R affinity and lipophilicity. However, in vitro stability of the PEG-containing compounds was significantly decreased. In addition, we confirmed that the tetrapeptide sequence H-Trp-Asp-(N-Me)Nle-1-Nal-NH₂ is indeed sufficient for high CCK-2R affinity.

CONCLUSION

We could demonstrate that a substitution of D-γ-Glu-Ala-Tyr-Gly by PEG spacers simplified the peptide structure of DOTA-MGS5 while high CCK-2R affinity and favorable lipophilicity were maintained. Nevertheless, further optimization with regard to metabolic stability must be carried out for these minigastrin analogs.

A bifunctional peptide-based fluorescent probe for ratiometric and "turn-on" detection of Zn(II) ions and its application in living cells

In this work, a bifunctional peptide-based fluorescent probe L containing a tetrapeptide scaffold (Pro-Gly-His-Trp-NH₂) and a dansyl group was synthesized using solid phase peptide synthesis (SPPS) technology. As designed, L, based on a FRET mechanism, exhibited high selectivity, excellent ratiometric signals, and fast response to Zn²⁺ in aqueous solutions at an excitation wavelength of 280 nm. In addition, when excited at 320 nm, L exhibited a fluorescent "turn-on" response towards Zn²⁺ based on PET mechanism. More importantly, the stoichiometry of L and Zn²⁺ was determined to be 2:1 by fluorescent titration, Job's plot method, and ESI-MS spectrometry. The association constant for Zn²⁺ ions was determined to be 6.26 × 10⁸ M^-2, while the limit of detection (LOD) of L was estimated as 5.43 nM, which is a much lower value than WHO and EPA guidelines for drinking water. Moreover, L was successfully applied to detect both Zn²⁺ and Cu²⁺ in living cells due to good biocompatibility and excellent low toxicity.

A study of tetrapeptide enantiomeric separation on crown ether based chiral stationary phases

The chiral separations of small peptides is an important challenge in the biological and medical sciences, because different stereoisomers of chiral drugs can often possess different pharmacological, pharmacokinetic, and/or toxicological activities. Commercially available crown ether chiral stationary phases based on S-(3,3'-diphenyl-1,1'-binaphthyl)-20-crown-6 (CROWNPAK CR-I (+)) and (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid (ChiroSil RCA (+)) have been successfully used for separating enantiomers of various racemic compounds containing primary amino groups. In this investigation, enantioresolution of more complex model analyte - tetrapeptide Tyr-Arg-Phe-Lys-NH₂, has been reported on crown ether chiral stationary phases. Organic and acidic modifier content in aqueous mobile phase was tested. All Tyr-Arg-Phe-Lys-NH₂ stereoisomers showed U-shaped retention plots, based on ACN content in mobile phase. Increased retention of tetrapeptide stereoisomers was observed at low (<35%) and at high (>70%) acetonitrile content in the mobile phase, indicating that different separation mechanisms are most likely involved. As a result, baseline separation of all eight tetrapeptide enantiomer pairs was achieved under isocratic elution mode on both chiral columns.

Influence of endomorphins along the pituitary-ovary axis in the Mozambique Tilapia Oreochromis mossambicus

Endomorphins (EM-1 and EM-2) are the tetrapeptides involved in pain and neuroendocrine responses with a high affinity for μ-opioid receptors in vertebrates. However, their role in fish reproduction is not clear. The aim of this study was to investigate the influence of EM-1 and EM-2 on the pituitary-ovary axis in the Mozambique tilapia Oreochromis mossambicus. The experimental set-up consisted of four groups, namely, initial controls, controls, EM-1- and EM-2-treated groups (n = 10 in each group consisting of two replicates). Although the number of stage IV (vitellogenic) follicles was significantly lower (P < 0.05) in controls compared to initial controls, the stage V (preovulatory) follicles were present in controls in contrast to their absence in initial controls. Treatment of 40 μg EM-1/0.1 ml saline/fish/day for 22 days resulted in significant increase (P < 0.05) in the number of stage I follicles compared to controls. While similar treatment of EM-2 did not significantly alter the number of stage I follicles compared to controls, the number of stage II follicles was significantly lower (P < 0.05) in this group compared to those of controls and EM-1 treated fish. The number of stage III and IV follicles did not significantly differ among controls, EM-1- and EM-2-treated groups. However, a significant reduction (P < 0.05) in the mean number of stage V follicles was observed in EM-1- and EM-2-treated fish compared to controls. These changes were concomitant with significant reduction (P < 0.05) in the intensity and the percent area of immunoreactivity of luteinizing hormone (LH) secreting cells in the proximal pars distalis (PPD) of the pituitary gland and significantly higher (P < 0.05) percent occurrence of follicular atresia in EM-1- and EM-2-treated fish compared to those of controls. Taken together, these results suggest an inhibitory effect for endomorphins along the pituitary-ovary axis, for the first time in fish.

Data of small peptides in SMILES and three-dimensional formats for virtual screening campaigns

The data presented in this article are structures of dipeptides, tripeptides and tetrapeptides constructed from all possible combinations of 20 natural and common amino acids. In total, the data contains 168400 peptides. The structures are available in their simplified molecular-input line-entry system (SMILES) and three-dimensional (3D) formats. The type of data are text files, which could be accessed and modified either by text editor applications (e.g. Notepad++) or by molecule visualization softwares (e.g., YASARA View). These structures could be used further in virtual screening campaigns in the early stage of drug discovery projects.

Advances and Challenges of HDAC Inhibitors in Cancer Therapeutics

Since the identification and cloning of human histone deacetylases (HDACs) and the rapid approval of vorinostat (Zolinza®) for the treatment of cutaneous T-cell lymphoma, the field of HDAC biology has met many initial successes. However, many challenges remain due to the complexity involved in the lysine posttranslational modifications, epigenetic transcription regulation, and nonepigenetic cellular signaling cascades. In this chapter, we will: review the discovery of the first HDAC inhibitor and present discussion regarding the future of next-generation HDAC inhibitors, give an overview of different classes of HDACs and their differences in lysine deacylation activity, discuss different classes of HDAC inhibitors and their HDAC isozyme preferences, and review HDAC inhibitors' preclinical studies, their clinical trials, their pharmacokinetic challenges, and future direction. We will also discuss the likely reason for the failure of multiple HDAC inhibitor clinical trials in malignancies other than lymphoma and multiple myeloma. In addition, the potential molecular mechanism(s) that may play a key role in the efficacy and therapeutic response rate in the clinic and the likely patient population for HDAC therapy will be discussed.

EGAR, A Food Protein-Derived Tetrapeptide, Reduces Seizure Activity in Pentylenetetrazole-Induced Epilepsy Models Through α-Amino-3-Hydroxy-5-Methyl-4-Isoxazole Propionate Receptors

A primary pathogeny of epilepsy is excessive activation of α-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptors (AMPARs). To find potential molecules to inhibit AMPARs, high-throughput screening was performed in a library of tetrapeptides in silico. Computational results suggest that some tetrapeptides bind stably to the AMPAR. We aligned these sequences of tetrapeptide candidates with those from in vitro digestion of the trout skin protein. Among salmon-derived products, Glu-Gly-Ala-Arg (EGAR) showed a high biological affinity toward AMPAR when tested in silico. Accordingly, natural EGAR was hypothesized to have anticonvulsant activity, and in vitro experiments showed that EGAR selectively inhibited AMPAR-mediated synaptic transmission without affecting the electrophysiological properties of hippocampal pyramidal neurons. In addition, EGAR reduced neuronal spiking in an in vitro seizure model. Moreover, the ability of EGAR to reduce seizures was evaluated in a rodent epilepsy model. Briefer and less severe seizures versus controls were shown after mice were treated with EGAR. In conclusion, the promising experimental results suggest that EGAR inhibitor against AMPARs may be a target for antiepilepsy pharmaceuticals. Epilepsy is a common brain disorder characterized by the occurrence of recurring, unprovoked seizures. Twenty to 30 % of persons with epilepsy do not achieve adequate seizure control with any drug. Here we provide a possibility in which a natural and edible tetrapeptide, EGAR, can act as an antiepileptic agent. We have combined computation with in vitro experiments to show how EGAR modulates epilepsy. We also used an animal model of epilepsy to prove that EGAR can inhibit seizures in vivo. This study suggests EGAR as a potential pharmaceutical for the treatment of epilepsy.

Ligand/kappa-opioid receptor interactions: insights from the X-ray crystal structure

During the past five years, the three-dimensional structures of 14 different G-protein coupled receptors (GPCRs) have been resolved by X-ray crystallography. The most recently published structures, those of the opioid receptors (ORs), are remarkably important in pain modulation, drug addiction, and mood disorders. These structures, confirmed previously proposed key interactions conferring potency and antagonistic properties, including the well-known interaction with Asp138, conserved in all aminergic GPCRs. In addition, crystallization of the opioid receptors highlighted the potential function of the ECL2 and ICL2 loops. We have previously reported a set of potent and selective kappa opioid receptor peptide agonists, of which ff(D-nle)r-NH₂ is among the most potent and selective ones. These peptides were identified from the deconvolution of a 6,250,000 tetrapeptide combinatorial library. A derivative of this set is currently the subject of a phase 2 clinical trial in the United States. In this work, we describe comparative molecular modeling studies of kappa-OR peptide agonists with the co-crystallized antagonist, JDTic, and also report structure-activity relationships of 23 tetrapeptides. The overall binding and contact interactions are sound and interactions known to favor selectivity and potency were observed. Additional modeling studies will reveal conformational changes that the kappa-OR undergoes upon binding to these peptide agonists.