Heme and Cu2+-induced vasoactive intestinal peptide (VIP) tyrosine nitration: A possible molecular mechanism for the attenuated anti-inflammatory effect of VIP in inflammatory diseases.

Vasoactive intestinal peptide (VIP) is a neuropeptide that play an important role in immunoregulation and anti-inflammation. Numerous inflammatory/autoimmune disorders are associated with decreased VIP binding ability to receptors and diminished VIP activation of cAMP generation in immune cells. However, the mechanisms linking oxidative/nitrative stress to VIP immune dysfunction remain unknown. It has been reported that the elevated heme or Cu2+ in inflammatory diseases can cause oxidative and nitrative damage to nearby biological targets under high oxidative stress conditions, which affects the structure and activity of linked peptides or proteins. Thus, the VIP down-regulated immune response may be interfered by redox metal catalyzed VIP tyrosine nitration. To explore this, we systematically investigated the possibility of heme or Cu2+ to catalyze VIP tyrosine nitration. The results showed that Tyr10 and Tyr22 of VIP can both be nitrated in heme/H2O2/NO2- system as well as in Cu2+/H2O2/NO2- system. Then, we used synthetic mutant VIPs with tyrosine residues substituted by 3-nitrotyrosine to study the impact of tyrosine nitration on VIP activity in SHSY-5Y cells. Our findings demonstrated that VIP nitration dramatically decreased the content of its α-helix and random coil, suggesting that VIP nitration might reduce its affinity to the receptor. This was further confirmed in the cAMP assay. The results showed that 10 nM of these tyrosine nitrated VIPs could significantly (p < 0.01) decrease cAMP secretion compared to the wild type VIP. Our data reveal that the attenuation of the neuroprotective effect of VIP in inflammation-related diseases might be attributed to metal-catalyzed VIP tyrosine nitration.

N-Heterocyclic Carbene-Palladium Polymers Network: Recyclable Pre-catalyst for Effective Suzuki-Miyaura Coupling Reaction in Water.

Rational design of high-efficiency N-heterocyclic carbene (NHC) palladium catalyst is of great importance to modern organic synthesis, especially in chemical and pharmaceutical industries. Herein, we fabricate a polymer network containing N-heterocyclic carbene palladium (PNNHC-Pd) catalytic active sites via an immobilization process. The N-heterocyclic carbene palladium can serve as a promising linkage of polymer network as well as an effective catalytic active site owing to its structural preference and strong σ-donating ability with palladium species. The results display that N-heterocyclic carbene palladium disperses homogeneously in polymer network, thus rendering PNNHC-Pd excellent catalytic activity, high stability and superior reusability in palladium-catalyzed Suzuki-Miyaura coupling reaction in aqueous medium. This work provides a new insight into the development of heterogenization of homogeneous catalysts based on polymer network.

Structure relationship of metalloporphyrins in inhibiting the aggregation of hIAPP.

Metalloporphyrins (FeTBAP, MnTBAP, FeTMPyP and MnTMPyP) have been proposed as effective therapeutic agents in ONOO--related disease including type 2 diabetes (T2D). As these metalloporphyrins share the structural similarities of the planar aromatic conjugation with a valuable class of inhibitors against amyloids fibrillation, they might be effective inhibitors via aromatic π-π stacking interactions with amyloid peptides. Here, we found that the anionic metalloporphyrins (FeTBAP and MnTBAP) are effective inhibitors against hIAPP fibrillation, while, the cationic metalloporphyrins (FeTMPyP and MnTMPyP) only have limited inhibitory effects. Besides, the porphyrin with iron center is more effective than the one with manganese center. Our results favor the electrostatic attraction contributes the main reason to the inhibitory effect between the anionic porphyrins and hIAPP, followed by the π-π stacking interactions between aromatic ring of porphyrins and hIAPP and the stronger coordination ability of iron center to hIAPP. Additionally, by comparison with FeTBAP, which can completely inhibit cytotoxicity induced by hIAPP via stabilizing hIAPP monomers, MnTBAP fails to reverse the cytotoxicity due to that it can only delay the transition of hIAPP from α-helix to ß-sheet rich oligomers. Our results provide theoretical significance for further designing or screening of metalloporphyrins as bifunctional antidiabetic drugs.

Y12 nitration of human calcitonin (hCT): A promising strategy to produce non-aggregation bioactive hCT.

Irreversible aggregation can extremely limit the bioavailability and therapeutic activity of peptide-based drugs. There is therefore an urgent demand of effective strategy to control peptide aggregation. Recently, we found that tyrosine nitration at certain sites of peptide can effectively inhibit its aggregation. This minor modification may be an ideal strategy to the rational design of peptide-based drugs with low aggregation propensity yet without loss of bioactivity. Human calcitonin (hCT) is such a peptide hormone known for its hypocalcaemic effect but has limited pharmaceutical potential due to a high tendency to aggregate. In this study, by using multiple techniques including Fluorescence, TEM, Nu-PAGE and CD, we demonstrated that Y12 nitration of hCT would significantly inhibit its self-assembles, and we also found that this modification would not only reduce the cytotoxicity induced by peptide aggregation, but also had little effect on its potency. This finding may provide a novel strategy for clinically application of hCT instead of sCT.

New Alternating Current Noise Analytics Enables High Discrimination in Gas Sensing.

Feature analysis has been increasingly considered as an important way to enhance the discrimination performance of gas sensors. In this work, a new analytical method based on alternating current noise spectrum is developed to discriminate chemically and structurally similar gases with remarkable performance. Compared with the conventional analytics based on the maximum, integral, and time of response, the noise spectrum of electrical response introduces a new informative feature to discriminate chemical gases. In experiment, three chemically and structurally similar gases, mesitylene, toluene, and o-xylene, are tested on ZnO thin film gas sensors. The result indicated that the noise analytics assisted by the support vector machine algorithm discriminated these similar gases with 94.2% in precision, about 20% higher than those obtained by conventional methods. Such a new alternating current noise analytics is very promising for application in sensors for high discrimination precision.

Heme prevents highly amyloidogenic human calcitonin (hCT) aggregation: A potential new strategy for the clinical reuse of hCT.

Irreversible aggregation can extremely limit the bioavailability and therapeutic activity of peptide-based drugs. Thus, peptide fibrillation is an excellent challenge for biotechnological drug development. Human calcitonin (hCT) is such a peptide hormone known for its hypocalcaemic effect but has limited pharmaceutical potential due to a high tendency to aggregate. hCT is therefore not widely used preparation in clinical practice. Nonetheless, hCT seems to be still an ideal target for clinical therapy when fibrillation is effectively inhibited, because the alternatives of hCT can stimulate undesirable immune responses in patients and cause side effects. Interestingly, heme is an essential component for many livings and has been shown a strong inhibitory effect on some amyloidogenic peptides aggregation. Here we demonstrate that it may be a most suitable, safe, biocompatible small molecule inhibitor on hCT aggregation, and thereby improving its activity when guiding the drug peptide in clinical therapeutics. In this work, we found that heme was able to reversibly bind with hCT to form a heme-hCT complex with a moderate binding constant (9.17 × 106 M-1) and significantly suppress the aggregation of hCT probably accomplished by heme binding to it, blocking the ß-sheet structure assembly which is essential in hCT fibril aggregation. Meanwhile, the heme-hCT complexes showed enhanced bioactivity compared to hCT itself after a 24 h incubation time in reducing blood calcium levels in mice. This study may develop a new strategy to reuse the wild-type hCT in clinical therapeutics.

Enhance the Discrimination Precision of Graphene Gas Sensors with a Hidden Markov Model.

Sensors are the key element to enable smart electronics and will play an important role in the emerging big data era. In this work, we reported an experimental study and a data-analytical characterization method to enhance the precision of discriminating chemically and structurally similar gases. Graphene sensors were fabricated by conventional photolithography and measured with feature analysis against different chemicals. A new hidden Markov model assisted with frequency spectral analysis, and the Gaussian mixture model (K-GMM-HMM) is developed to discriminate similar gases. The results indicated that the new method achieved a high prediction accuracy of 94%, 27% higher than the maximum value obtained by the conventional methods or other feature transient analysis methods. This study indicated that graphene gas sensors with the new K-GMM-HMM analysis are very attractive for chemical discrimination used in future smart electronics.

Copper Binding Induces Nitration of NPY under Nitrative Stress: Complicating the Role of NPY in Alzheimer's Disease.

Neuropeptide Y (NPY) is a 36 amino acid peptide that regulates a multitude of physiological functions in the central nervous system and has been shown to be involved in Alzheimer's disease (AD). A change in copper homeostasis is a remarkable feature of AD, and the dysregulation may contribute to toxicity in neural cells. Moreover, it has been shown that copper could interact with many neuropeptides and result in catalyzing the production of reactive oxygen species, which may lead to peptide oxidation. Besides, copper could also catalyze protein tyrosine nitration under oxidative stress, and there are two tyrosine residues playing an important role in NPY. Therefore, it is also likely that copper has an action on NPY and potentially influences its functions through tyrosine nitration. In this paper, the studies of the interaction of copper with NPY and the copper-catalyzed NPY nitration were performed. The electrochemical techniques, UV-vis spectroscopy, mass spectrometry, and fluorescence titration, have been applied to show that copper can interact with NPY to form a Cu-NPY complex with a conditional dissociation constant of 0.021 µmol/L, and the binding promotes the generation of •OH. Dot blotting results reveal that NPY can be nitrated upon binding with copper under nitrative stress. Furthermore, liquid chromatography-mass spectrometry (LC-MS) identify that the tyrosine residues in NPY are all nitrated during the nitration process, which will cause the inactivation of NPY shown by our previous study. This study supports the hypothesis that copper has a close correlation with NPY and implicates the peptide in AD. These data may provide a new insight into understanding the pathology and pathogenesis of AD.

NPY binds with heme to form a NPY-heme complex: enhancing peroxidase activity in free heme and promoting NPY nitration and inactivation.

Neuropeptide Y (NPY) is a member of the pancreatic peptide family of neuropeptides that play a crucial role in numerous central and peripheral nervous system responses. Recently, it has been shown that NPY protects cells against neurotoxic damage from ß-amyloid peptides (Aß) in Alzheimer's disease (AD). Heme is a common factor linking several metabolic perturbations in AD and altered heme metabolism has been shown to be related to the pathologies of AD. Thus, heme may have a chance to act on NPY and potentially counteract its function. To explore this, UV-visible spectroscopy, fluorescence spectroscopy and differential pulse voltammetry (DPV) were used to demonstrate that NPY can bind with heme to form a NPY-heme complex and the binding enhances the peroxidase activity of heme. Dot blotting results indicate that NPY is easily nitrated upon binding with heme when H2O2 and NO2- are present. Furthermore, LC-MS/MS results confirm that tyrosine36 (Tyr36), an important amino acid residue of NPY in binding and activating neuropeptide receptors, can be nitrated during the nitration process. Thereafter, we used mutant peptide NPY(3N) (Tyr36 replaced by 3-nitrotyrosine) to investigate the impact of nitration on the structure and bioactivity of the peptide. Our results show that Tyr36 nitration destabilizes the α-helix conformation of the peptide, and counteracts NPY-induced inhibition of cAMP accumulation in SK-N-MC cells. Collectively, these data imply that the self-association of NPY with heme potentially induces tyrosine nitration, destroys the active monomeric conformation of the peptide and thereby counteracts its bioactivity.

Two-dimensional hybrid layered materials: strain engineering on the band structure of MoS2/WSe2 hetero-multilayers.

In this paper, we report a comprehensive modeling and simulation study of constructing hybrid layered materials by alternately stacking MoS2 and WSe2 monolayers. Such hybrid MoS2/WSe2 hetero-multilayers exhibited direct bandgap semiconductor characteristics with bandgap energy (E g) in a range of 0.45-0.55 eV at room temperature, very attractive for optoelectronics (wavelength range 2.5-2.75 µm) based on thicker two-dimensional (2D) materials. It was also found that the interlayer distance has a significant impact on the electronic properties of the hetero-multilayers, for example a five orders of magnitude change in the conductance was observed. Three material phases, direct bandgap semiconductor, indirect bandgap semiconductor, and metal were observed in MoS2/WSe2 hetero-multilayers, as the interlayer distance decreased from its relaxed (i.e., equilibrium) value of about 6.73 Å down to 5.50 Å, representing a vertical pressure of about 0.8 GPa for the bilayer and 1.5 GPa for the trilayer. Such new hybrid layered materials are very interesting for future nanoelectronic pressure sensor and nanophotonic applications. This study describes a new approach to explore and engineer the construction and application of tunable 2D semiconductors.