Bromo-spiroisoxazoline Alkaloids, Including an Isoserine Peptide, from the Caribbean Marine Sponge Aplysina lacunosa

Three new bromotyrosine spiroisoxazoline alkaloids, lacunosins A and B (1 and 2) and desaminopurealin (3), were isolated from a MeOH extract of the marine sponge Aplysina lacunosa that showed modest α-chymotrypsin inhibitory activity. The structures of 1-3 share the spirocyclohexadienyl-isoxazoline ring system found in purealidin-R and several other Verongid sponge secondary metabolites. Compounds 1 and 2 are coupled to a glycine and an isoserine methyl ester, respectively. Alkaloid 3 is linked, contiguously, to an O-1-aminopropyl 3,5-dibromotyrosyl ether and, finally, to histamine through an amide bond. The planar structures of all three compounds were obtained from analysis of MS and 1D and 2D NMR data. The absolute configuration of the SIO unit of 1-3 was assigned by electronic circular dichroism (ECD). The isoserine amino acid residue in 2 was found to be a 1:1 mixture of epimers using a new Marfey's type reagent, derived from Trp-NH2. Allylic O-naphthoylation of the SIO subunit enhances the ECD spectrum of SIOs and improves discrimination of enantiomorphs. A unifying hypothesis is proposed that links the biosynthesis of several of the new compounds with previously reported analogues.

Prognostic Value of O-(2-[18F]Fluoroethyl)-L-Tyrosine PET/CT in Newly Diagnosed WHO 2016 Grade II and III Glioma

PURPOSE

The use of [¹⁸F]fluoroethyl)-L-tyrosine ([¹⁸F]FET) positron emission tomography/computed tomography (PET/CT) has proven valuable in brain tumor management. This study aimed to investigate the prognostic value of radiotracer uptake in newly diagnosed grade II or III gliomas according to the current 2016 World Health Organization (WHO) classification.

PROCEDURES

A total of 35 treatment-naive patients (mean age, 48 ± 17 years) with histologically proven WHO grade II or III gliomas as defined by the current 2016 WHO classification were included. Static PET/CT imaging was performed 20 min after intravenous [¹⁸F]FET injection. Images were assessed visually and semi-quantitatively using regions of interest for both tumor (SUVmax, SUVmean) and background (BKGmean) to calculate tumor-to-background (TBR) ratios. The association among histological results, molecular markers (including isocitrate dehydrogenase enzyme and methylguanine-DNA methyltransferase status), clinical features (age), and PET findings was tested and compared with outcome (progression-free [PFS] and overall survival [OS]).

RESULTS

Fourteen patients presented with grade II (diffuse astrocytoma n = 10, oligodendroglioma n = 4) and 21 patients with grade III glioma (anaplastic astrocytoma n = 15, anaplastic oligodendroglioma n = 6). Twenty-seven out of the 35 patients were PET-positive (grade II n = 8/14, grade III n = 19/21), with grade III tumors exhibiting significantly higher amino acid uptake (TBR_mean and TBR_max; p = 0.03 and p = 0.02, respectively). PET-negative lesions demonstrated significantly prolonged PFS (p = 0.003) as compared to PET-positive gliomas. PET-positive disease had a complementary value in prognostication in addition to patient age, glioma grade, and molecular markers.

CONCLUSIONS

Amino acid uptake as assessed by [¹⁸F]FET-PET/CT imaging is useful as non-invasive read-out for tumor biology and prognosis in newly diagnosed, treatment-naive gliomas according to the 2016 WHO classification.

Tyrosinase Inhibition and Kinetic Details of Puerol A Having But-2-Enolide Structure from Amorpha fruticosa

Puerol A (1) from Amorpha fruticosa showed highly potent inhibition against both monophenolase (IC₅₀ = 2.2 μM) and diphenolase (IC₅₀ = 3.8 μM) of tyrosinase. We tried to obtain a full story of enzyme inhibitory behavior for inhibitor 1 because the butenolide skeleton has never been reported as a tyrosinase inhibitor. Puerol A was proved as a reversible, competitive, simple slow-binding inhibitor, according to the respective parameters; k₃ = 0.0279 μM⁻¹ min⁻¹ and k₄ = 0.003 min⁻¹. A longer lag-phase and a reduced static-state activity of the enzyme explained that puerol A had a tight formation of the complex with E_met. Dose-dependent inhibition was also confirmed by high-performance liquid chromatography (HPLC) analysis using N-acetyl-l-tyrosine as a substrate, which was completely inhibited at 20 μM. A high binding affinity of 1 to tyrosinase was confirmed by fluorescence quenching analysis. Moreover, puerol A decreased melanin content in the B16 melanoma cell dose-dependently with an IC₅₀ of 11.4 μM.

A Trifunctional Linker for Palmitoylation and Peptide and Protein Localization in Biological Membranes

Attachment of lipophilic groups is an important post-translational modification of proteins, which involves the coupling of one or more anchors such as fatty acids, isoprenoids, phospholipids, or glycosylphosphatidyl inositols. To study its impact on the membrane partitioning of hydrophobic peptides or proteins, we designed a tyrosine-based trifunctional linker. The linker allows the facile incorporation of two different functionalities at a cysteine residue in a single step. We determined the effect of the lipid modification on the membrane partitioning of the synthetic α-helical model peptide WALP with or without here and in all cases below; palmitoyl groups in giant unilamellar vesicles that contain a liquid-ordered (Lo ) and liquid-disordered (Ld ) phase. Introduction of two palmitoyl groups did not alter the localization of the membrane peptides, nor did the membrane thickness or lipid composition. In all cases, the peptide was retained in the Ld phase. These data demonstrate that the Lo domain in model membranes is highly unfavorable for a single membrane-spanning peptide.

Differential Proliferation Effect of the Newly Synthesized Valine, Tyrosine and Tryptophan-Naphthoquinones in Immortal and Tumorigenic Cervical Cell Lines

We previously showed that microwave assisted synthesis is the best method for the synthesis of naphthoquinone amino acid and chloride-naphthoquinone amino acid derivatives by a complete evaluation of reaction conditions such as stoichiometry, bases, and pH influence. Following the same strategy, we synthesized chloride and non-chloride tyrosine, valine, and tryptophan-naphthoquinones achieving 85–95%, 80–92%, and 91–95% yields, respectively. The cyclic voltammetry profiles showed that both series of naphthoquinone amino acid derivatives mainly display one redox reaction process. Overall, chloride naphthoquinone amino acid derivatives exhibited redox potential values (E_1/2) more positive than non-chloride compounds. The six newly synthesized compounds were tested in HPV positive and negative as well as in immortal and tumorigenic cell lines to observe the effects in different cellular context simulating precancerous and cancerous status. A dose-response was achieved to determine the IC50 of six newly synthesized compounds in SiHa (Tumorigenic and HPV16 positive), CaLo (Tumorigenic and HPV18 positive), C33-A (Tumorigenic and HPV negative) and HaCaT (Keratinocytes immortal HPV negative) cell lines. Non-chloride tryptophan-naphthoquinone (3c) and chloride tyrosine-naphthoquine (4a) effects were more potent in tumorigenic SiHa, CaLo, and C33-A cells with respect to non-tumorigenic HaCaT cells. Interestingly, there seems to be a differential effect in non-chloride and chloride naphthoquinone amino acid derivatives in tumorigenic versus non tumorigenic cells. Considering all naphthoquinone amino acid derivatives that our group synthesized, it seems that hydrophobic and aromatic amino acids have the greatest effect on cell proliferation inhibition. These results show promising compounds for cervical cancer treatment.

Purification and Biochemical Characterization of a Tyrosine Phenol-lyase from Morganella morganii

Tyrosine phenol-lyase (TPL) is a valuable and cost-effective biocatalyst for the biosynthesis of L-tyrosine and its derivatives, which are valuable intermediates in the pharmaceutical industry. A TPL from Morganella morganii (Mm-TPL) was overexpressed in Escherichia coli and characterized. Mm-TPL was determined as a homotetramer with molecular weight of 52 kDa per subunit. Its optimal temperature and pH for β-elimination of L-tyrosine were 45 °C and pH 8.5, respectively. Mm-TPL manifested strict substrate specificity for the reverse reaction of β-elimination and ortho- and meta-substituted phenols with small steric size were preferred substrates. The enzyme showed excellent catalytic performance for synthesis of L-tyrosine, 3-fluoro-L-tyrosine, and L-DOPA with a yield of 98.1%, 95.1%, and 87.2%, respectively. Furthermore, the fed-batch bioprocess displayed space-time yields of 9.6 g L^-1 h^-1 for L-tyrosine and 4.2 g L^-1 h^-1 for 3-fluoro-L-tyrosine with a yield of 67.4 g L^-1 and 29.5 g L^-1, respectively. These results demonstrated the great potential of Mm-TPL for industrial application.

Tyrosine-Chlorambucil Conjugates Facilitate Cellular Uptake through L-Type Amino Acid Transporter 1 (LAT1) in Human Breast Cancer Cell Line MCF-7

l-type amino acid transporter 1 (LAT1) is an amino acid transporter that is overexpressed in several types of cancer and, thus, it can be a potential target for chemotherapy. The objectives of this study were to (a) synthesize LAT1-targeted chlorambucil derivatives and (b) evaluate their LAT1-mediated cellular uptake as well as antiproliferative activity in vitro in the human breast cancer MCF-7 cell line. Chlorambucil was conjugated to l-tyrosine—an endogenous LAT1 substrate—via either ester or amide linkage (compounds 1 and 2, respectively). While chlorambucil itself did not bind to LAT1, its derivatives 1 and 2 bound to LAT1 with a similar affinity as with l-tyrosine and their respective cellular uptake was significantly higher than that of chlorambucil in MCF-7. The results of our cellular uptake study are indicative of antiproliferative activity, as a higher intracellular uptake of chlorambucil derivatives resulted in greater cytotoxicity than chlorambucil by itself. LAT1 thus contributes to intracellular uptake of chlorambucil derivatives and, therefore, increases antiproliferative activity. The understanding gained from our research can be used in the development of LAT1-targeted anticancer drugs and prodrugs for site-selective and enhanced chemotherapeutic activity.

Tyrosinase-Mediated Oxidative Coupling of Tyrosine Tags on Peptides and Proteins

Oxidative coupling (OC) through o-quinone intermediates has been established as an efficient and site-selective way to modify protein N-termini and the unnatural amino acid p-aminophenylalanine (paF). Recently, we reported that the tyrosinase-mediated oxidation of phenol-tagged cargo molecules is a particularly convenient method of generating o-quinones in situ. The coupling partners can be easily prepared and stored, the reaction takes place under mild conditions (phosphate buffer, pH 6.5, 4 to 23 °C), and dissolved oxygen is the only oxidant required. Here, we show an important extension of this chemistry for the activation of tyrosine residues that project into solution from the N or C-termini of peptide and protein substrates. Generating the o-quinone electrophiles from tyrosine allows greater flexibility in choosing the nucleophilic coupling partner and expands the scope of the reaction to include C-terminal positions. We also introduce a new bacterial tyrosinase enzyme that shows improved activation for some tyrosine substrates. The efficacy of several secondary amines and aniline derivatives was evaluated in the coupling reactions, providing important information for coupling partner design. This strategy was used to modify the C-termini of an antibody scFv construct and of Protein L, a human IgG kappa light chain binding protein. The use of the modified proteins as immunolabeling agents was also demonstrated.

Molecular basis for receptor tyrosine kinase A-loop tyrosine transphosphorylation

A long-standing mystery shrouds the mechanism by which catalytically repressed receptor tyrosine kinase domains accomplish transphosphorylation of activation loop (A-loop) tyrosines. Here we show that this reaction proceeds via an asymmetric complex that is thermodynamically disadvantaged because of an electrostatic repulsion between enzyme and substrate kinases. Under physiological conditions, the energetic gain resulting from ligand-induced dimerization of extracellular domains overcomes this opposing clash, stabilizing the A-loop-transphosphorylating dimer. A unique pathogenic fibroblast growth factor receptor gain-of-function mutation promotes formation of the complex responsible for phosphorylation of A-loop tyrosines by eliminating this repulsive force. We show that asymmetric complex formation induces a more phosphorylatable A-loop conformation in the substrate kinase, which in turn promotes the active state of the enzyme kinase. This explains how quantitative differences in the stability of ligand-induced extracellular dimerization promotes formation of the intracellular A-loop-transphosphorylating asymmetric complex to varying extents, thereby modulating intracellular kinase activity and signaling intensity.

Honey as Source of Nitrogen Compounds: Aromatic Amino Acids, Free Nucleosides and Their Derivatives

The content of selected major nitrogen compounds including nucleosides and their derivatives was evaluated in 75 samples of seven varieties of honey (heather, buckwheat, black locust, goldenrod, canola, fir, linden) by targeted ultra-high performance liquid chromatography-diode array detector - high-resolution quadrupole time-of-flight mass spectrometry (UHPLC-DAD-QqTOF-MS) and determined by UHPLC-DAD. The honey samples contained nucleosides, nucleobases and their derivatives (adenine: 8.9 to 18.4 mg/kg, xanthine: 1.2 to 3.3 mg/kg, uridine: 17.5 to 51.2 mg/kg, guanosine: 2.0 to 4.1 mg/kg; mean amounts), aromatic amino acids (tyrosine: 7.8 to 263.9 mg/kg, phenylalanine: 9.5 to 64.1 mg/kg; mean amounts). The amounts of compounds significantly differed between some honey types. For example, canola honey contained a much lower amount of uridine (17.5 ± 3.9 mg/kg) than black locust where it was most abundant (51.2 ± 7.8 mg/kg). The presence of free nucleosides and nucleobases in different honey varieties is reported first time and supports previous findings on medicinal activities of honey reported in the literature as well as traditional therapy and may contribute for their explanation. This applies, e.g., to the topical application of honey in herpes infections, as well as its beneficial activity on cognitive functions as nootropic and neuroprotective, in neuralgia and is also important for the understanding of nutritional values of honey.

NMR Observation of Intermolecular Hydrogen Bonds between Protein Tyrosine Side-Chain OH and DNA Phosphate Groups

Hydrogen bonds between protein side-chain hydroxyl (OH) and phosphate groups are one of the most common types of intermolecular hydrogen bonds in protein-DNA/RNA complexes. Using NMR spectroscopy, we identified and characterized the hydrogen bonds between tyrosine side-chain OH and DNA phosphate groups in a protein-DNA complex. These OH groups exhibited relatively slow hydrogen-exchange rates and sizable scalar couplings between hydroxyl 1H and DNA phosphate 31P nuclei across the hydrogen bonds. Information about intermolecular hydrogen bonds facilitates investigations of the DNA/RNA recognition by the protein.

Valence and patterning of aromatic residues determine the phase behavior of prion-like domains

Prion-like domains (PLDs) can drive liquid-liquid phase separation (LLPS) in cells. Using an integrative biophysical approach that includes nuclear magnetic resonance spectroscopy, small-angle x-ray scattering, and multiscale simulations, we have uncovered sequence features that determine the overall phase behavior of PLDs. We show that the numbers (valence) of aromatic residues in PLDs determine the extent of temperature-dependent compaction of individual molecules in dilute solutions. The valence of aromatic residues also determines full binodals that quantify concentrations of PLDs within coexisting dilute and dense phases as a function of temperature. We also show that uniform patterning of aromatic residues is a sequence feature that promotes LLPS while inhibiting aggregation. Our findings lead to the development of a numerical stickers-and-spacers model that enables predictions of full binodals of PLDs from their sequences.

The structure of human thyroglobulin

Thyroglobulin (TG) is the protein precursor of thyroid hormones, which are essential for growth, development and the control of metabolism in vertebrates1,2. Hormone synthesis from TG occurs in the thyroid gland via the iodination and coupling of pairs of tyrosines, and is completed by TG proteolysis3. Tyrosine proximity within TG is thought to enable the coupling reaction but hormonogenic tyrosines have not been clearly identified, and the lack of a three-dimensional structure of TG has prevented mechanistic understanding4. Here we present the structure of full-length human thyroglobulin at a resolution of approximately 3.5 Å, determined by cryo-electron microscopy. We identified all of the hormonogenic tyrosine pairs in the structure, and verified them using site-directed mutagenesis and in vitro hormone-production assays using human TG expressed in HEK293T cells. Our analysis revealed that the proximity, flexibility and solvent exposure of the tyrosines are the key characteristics of hormonogenic sites. We transferred the reaction sites from TG to an engineered tyrosine donor-acceptor pair in the unrelated bacterial maltose-binding protein (MBP), which yielded hormone production with an efficiency comparable to that of TG. Our study provides a framework to further understand the production and regulation of thyroid hormones.

hNGF Peptides Elicit the NGF-TrkA Signalling Pathway in Cholinergic Neurons and Retain Full Neurotrophic Activity in the DRG Assay

In the last decade, Nerve Growth Factor (NGF)-based clinical approaches have lacked specific and efficient Tyrosine Kinase A (TrkA) agonists for brain delivery. Nowadays, the characterization of novel small peptidomimetic is taking centre stage in preclinical studies, in order to overcome the main size-related limitation in brain delivery of NGF holoprotein for Central Nervous System (CNS) pathologies. Here we investigated the NGF mimetic properties of the human NGF 1–14 sequence (hNGF1–14) and its derivatives, by resorting to primary cholinergic and dorsal root ganglia (DRG) neurons. Briefly, we observed that: 1) hNGF1–14 peptides engage the NGF pathway through TrkA phosphorylation at tyrosine 490 (Y490), and activation of ShcC/PI3K and Plc-γ/MAPK signalling, promoting AKT-dependent survival and CREB-driven neuronal activity, as seen by levels of the immediate early gene c-Fos, of the cholinergic marker Choline Acetyltransferase (ChAT), and of Brain Derived Neurotrophic Factor (BDNF); 2) their NGF mimetic activity is lost upon selective TrkA inhibition by means of GW441756; 3) hNGF1–14 peptides are able to sustain DRG survival and differentiation in absence of NGF. Furthermore, the acetylated derivative Ac-hNGF1–14 demonstrated an optimal NGF mimetic activity in both neuronal paradigms and an electrophysiological profile similar to NGF in cholinergic neurons. Cumulatively, the findings here reported pinpoint the hNGF1–14 peptide, and in particular its acetylated derivative, as novel, specific and low molecular weight TrkA specific agonists in both CNS and PNS primary neurons.

Characterization of the metabolites of GW1929 in rat by liquid chromatography coupled with electrospray ionization tandem mass spectrometry

RATIONALE

GW1929 is a potent PPAR-γ activator. To fully understand its mechanism of action, it is necessary to study the in vitro and in vivo metabolism.

METHODS

For in vitro metabolism, GW1929 was incubated with rat hepatocytes at 37°C for 2 h. For in vivo metabolism, rats were orally administered with GW1929 at a single dose of 10 mg/kg and plasma, urinary and fecal samples were collected at defined time points. All the samples were analyzed by the developed ultra-high-performance liquid chromatography combined with tandem mass spectrometry. The structures of metabolites were proposed according to their accurate masses and product ions.

RESULTS

A total of 17 metabolites, including seven glucuronide conjugates, were detected and structurally identified. M4 (hydroxylation), M13 (demethylation) and M14 (hydroxylation) were the most abundant metabolites. The metabolic pathways of GW1929 referred to hydroxylation, demethylation, deamination and glucuronidation.

CONCLUSIONS

The present study provided new information on the in vitro and in vivo metabolic profiles of GW1929 which will be helpful for a better understanding of the mechanism of the elimination of GW1929.

Intermittent hypoxia mediated by TSP1 dependent on STAT3 induces cardiac fibroblast activation and cardiac fibrosis

Intermittent hypoxia (IH) is the predominant pathophysiological disturbance in obstructive sleep apnea (OSA), known to be independently associated with cardiovascular diseases. However, the effect of IH on cardiac fibrosis and molecular events involved in this process are unclear. Here, we tested IH in angiotensin II (Ang II)-induced cardiac fibrosis and signaling linked to fibroblast activation. IH triggered cardiac fibrosis and aggravated Ang II-induced cardiac dysfunction in mice. Plasma thrombospondin-1 (TSP1) content was upregulated in both IH-exposed mice and OSA patients. Moreover, both in vivo and in vitro results showed IH-induced cardiac fibroblast activation and increased TSP1 expression in cardiac fibroblasts. Mechanistically, phosphorylation of STAT3 at Tyr705 mediated the IH-induced TSP1 expression and fibroblast activation. Finally, STAT3 inhibitor S3I-201 or AAV9 carrying a periostin promoter driving the expression of shRNA targeting Stat3 significantly attenuated the synergistic effects of IH and Ang II on cardiac fibrosis in mice. This work suggests a potential therapeutic strategy for OSA-related fibrotic heart disease.

The toxicity of non-aged and aged coated silver nanoparticles to the freshwater shrimp Paratya australiensis

Nanoparticles (NPs) transform in the environment which result in alterations to their physicochemical properties. However, the effects of aging on the toxicity of NPs to aquatic organisms remain to be determined. Further the reports that have been published present contradictory results. The aim of this study was to examine the stability of differently coated silver nanoparticles (AgNPs) in media and the influence of aging of these NP on potential toxicity to freshwater shrimp Paratya australiensis. Coating-dependent changes in the stability of AgNP were observed with aging. Curcumin (C) coated AgNPs were stable, while tyrosine (T) coated AgNPs and epigallocatechin gallate (E) coated AgNPs aggregated in the P. australiensis medium. Increased lipid peroxidation and catalase activity was noted in P. australiensis exposed to AgNPs, suggesting oxidative stress was associated with NP exposure. The enhanced oxidative stress initiated by aged C-AgNPs suggests that aging of these NPs produced different toxicological responses. In summary, data suggest that coating-dependent alterations in NPs, together with aging affect both persistence and subsequent toxicity of NPs to freshwater organisms. Thus, the coating-dependent fate and toxicity of AgNPs together with the effect of their aging need to be considered in assessing the environmental risk of AgNPs to aquatic organisms.

2-Fluorotyrosine is a valuable but understudied amino acid for protein-observed 19F NMR

Incorporation of ¹⁹F into proteins allows for the study of their molecular interactions via NMR. The study of ¹⁹F labeled aromatic amino acids has largely focused on 4-,5-, or 6-fluorotryptophan, 4-fluorophenylalanine, (4,5, or 6FW) or 3-fluorotyrosine (3FY), whereas 2-fluorotyrosine (2FY) has remained largely understudied. Here we report a comparative analysis with different fluorinated amino acids. We first report the NMR chemical shift responsiveness of five aromatic amino acid mimics to changes in solvent polarity and find that the most responsive, a mimic of 3FY, has a 2.9-fold greater change in chemical shift compared to the other amino acid mimics in aprotic solvents including the 2FY mimic. We also probed the utility of 2FY for ¹⁹F NMR by measuring its NMR relaxation properties in solution and the chemical shift anisotropy (CSA) of a polycrystalline sample of the amino acid by magic angle spinning. Using protein-observed fluorine NMR (PrOF NMR), we compared the influence of 2FY and 3FY incorporation on stability and pK_a perturbation when incorporated into the KIX domain of CBP/p300. Lastly, we investigated the ¹⁹F NMR response of both 2FY and 3FY-labeled proteins to a protein-protein interaction partner, MLL, and discovered that 2FY can report on allosteric interactions that are not observed with 3FY-labeling in this protein complex. The reduced perturbation to pK_a and similar but reduced CSA of 2FY to 3FY supports 2FY as a suitable alternative amino acid for incorporation into large proteins for ¹⁹F NMR analysis.

Site-Specific Encoding of Photoactivity in Antibodies Enables Light-Mediated Antibody-Antigen Binding on Live Cells

Antibodies have found applications in several fields, including, medicine, diagnostics, and nanotechnology, yet methods to modulate antibody-antigen binding using an external agent remain limited. Here, we have developed photoactive antibody fragments by genetic site-specific replacement of single tyrosine residues with photocaged tyrosine, in an antibody fragment, 7D12. A simple and robust assay is adopted to evaluate the light-mediated binding of 7D12 mutants to its target, epidermal growth factor receptor (EGFR), on the surface of cancer cells. Presence of photocaged tyrosine reduces 7D12-EGFR binding affinity by over 20-fold in two out of three 7D12 mutants studied, and binding is restored upon exposure to 365 nm light. Molecular dynamics simulations explain the difference in effect of photocaging on 7D12-EGFR interaction among the mutants. Finally, we demonstrate the application of photoactive antibodies in delivering fluorophores to EGFR-positive live cancer cells in a light-dependent manner.

Palm Fruit Bioactives augment expression of Tyrosine Hydroxylase in the Nile Grass Rat basal ganglia and alter the colonic microbiome

Tyrosine hydroxylase (TH) catalyzes the hydroxylation of L-tyrosine to L-DOPA. This is the rate-limiting step in the biosynthesis of the catecholamines - dopamine (DA), norepinephrine (NE), and epinephrine (EP). Catecholamines (CA) play a key role as neurotransmitters and hormones. Aberrant levels of CA are associated with multiple medical conditions, including Parkinson's disease. Palm Fruit Bioactives (PFB) significantly increased the levels of tyrosine hydroxylase in the brain of the Nile Grass rat (NGR), a novel and potentially significant finding, unique to PFB among known botanical sources. Increases were most pronounced in the basal ganglia, including the caudate-putamen, striatum and substantia nigra. The NGR represents an animal model of diet-induced Type 2 Diabetes Mellitus (T2DM), exhibiting hyperglycemia, hyperinsulinemia, and insulin resistance associated with hyperphagia and accelerated postweaning weight gain induced by a high-carbohydrate diet (hiCHO). The PFB-induced increase of TH in the basal ganglia of the NGR was documented by immuno-histochemical staining (IHC). This increase in TH occurred equally in both diabetes-susceptible and diabetes-resistant NGR fed a hiCHO. PFB also stimulated growth of the colon microbiota evidenced by an increase in cecal weight and altered microbiome.  The metabolites of colon microbiota, e.g. short-chain fatty acids, may influence the brain and behavior significantly.

Grafting versus Crosslinking of Silk Fibroin-g-PNIPAM via Tyrosine-NIPAM Bridges

This paper reports the synthesis and complex characterization of novel polymeric networks based on the crosslinking of Bombyx mori silk fibroin via poly(N-isopropylacrylamide) bridges generated by an ammonium cerium nitrate redox system. The research study gives an understanding of the polymerization mechanism in terms of the generation of radical sites, radical growth and termination reaction, as well as the involvement of modifications on silk fibroin structure and properties. The physico-chemical characterization was carried out by FTIR-ATR, X-ray photoelectron spectroscopy and RAMAN spectroscopy with unravelling the chemical modification. The structural characterization and spatial arrangement by secondary structure were carried out by X-ray diffraction and circular dichroism. The thermal behavior and thermal stability were evaluated by differential scanning calorimetry and thermogravimetric analysis. The novel complex polymer network is intended to be used in the field of smart drug delivery systems.

Binding of rose bengal to lysozyme modulates photooxidation and cross-linking reactions involving tyrosine and tryptophan

This work examined the hypothesis that interactions of Rose Bengal (RB^2-) with lysozyme (Lyso) might mediate type 1 photoreactions resulting in protein cross-linking even under conditions favoring ¹O₂ formation. UV-visible spectrophotometry, isothermal titration calorimetry (ITC), and docking analysis were employed to characterize RB^2--Lyso interactions, while oxidation of Lyso was studied by SDS-PAGE gels, extent of amino acid consumption, and liquid chromatography (LC) with mass detection (employing tryptic peptides digested in H₂¹⁸O and H₂O). Docking studies showed five interaction sites including the active site. Hydrophobic interactions induced a red shift of the visible spectrum of RB^2- giving a K_d of 4.8 μM, while data from ITC studies, yielded a K_d of 0.68 μM as an average of the interactions with stoichiometry of 3.3 RB^2- per Lyso. LC analysis showed a high consumption of readily-oxidized amino acids (His, Trp, Met and Tyr) located at different and diverse locations within the protein. This appears to reflect extensive damage on the protein probably mediated by a type 2 (¹O₂) mechanism. In contrast, docking and mass spectrometry analysis provided evidence for the generation of specific intra- (Tyr23-Tyr20) and inter-molecular (Tyr23-Trp62) Lyso cross-links, and Lyso dimer formation via radical-radical, type 1 mechanisms.

Absolute Quantitation of Oxidizable Peptides by Coulometric Mass Spectrometry

Quantitation methods for peptides using mass spectrometry have advanced rapidly. These methods rely on using standard and/or isotope-labeled peptides, which might be difficult or expensive to synthesize. To tackle this challenge, we present a new approach for absolute quantitation without the use of standards or calibration curves based on coulometry combined with mass spectrometry (MS). In this approach, which we call coulometric mass spectrometry (CMS), the mass spectrum of a target peptide containing one or more tyrosine residues is recorded before and after undergoing electrochemical oxidation. We record the total integrated oxidation current from the electrochemical measurement, which according to the Faraday's Law of coulometry, provides the number of moles of oxidized peptide. The ion intensity ratio of the target peptide before and after oxidation provides an excellent estimate of the fraction of the peptide that has been oxidized, from which the total amount of peptide is calculated. The striking strength of CMS is that it needs no standard peptide, but CMS does require the peptide to contain a known number of oxidizable groups. To illustrate the power of this method, we analyzed various tyrosine-containing peptides such as GGYR, DRVY, oxytocin, [Arg⁸]-vasotocin and angiotensinogen 1-14 with a quantification error ranging from - 7.5 to + 2.4%. This approach is also applicable to quantifying phosphopeptides and could be useful in proteomics research.

Naturally Drug-Loaded Chitin: Isolation and Applications

Naturally occurring three-dimensional (3D) biopolymer-based matrices that can be used in different biomedical applications are sustainable alternatives to various artificial 3D materials. For this purpose, chitin-based structures from marine sponges are very promising substitutes. Marine sponges from the order Verongiida (class Demospongiae) are typical examples of demosponges with well-developed chitinous skeletons. In particular, species belonging to the family Ianthellidae possess chitinous, flat, fan-like fibrous skeletons with a unique, microporous 3D architecture that makes them particularly interesting for applications. In this work, we focus our attention on the demosponge Ianthella flabelliformis (Linnaeus, 1759) for simultaneous extraction of both naturally occurring ("ready-to-use") chitin scaffolds, and biologically active bromotyrosines which are recognized as potential antibiotic, antitumor, and marine antifouling substances. We show that selected bromotyrosines are located within pigmental cells which, however, are localized within chitinous skeletal fibers of I. flabelliformis. A two-step reaction provides two products: treatment with methanol extracts the bromotyrosine compounds bastadin 25 and araplysillin-I N20 sulfamate, and a subsequent treatment with acetic acid and sodium hydroxide exposes the 3D chitinous scaffold. This scaffold is a mesh-like structure, which retains its capillary network, and its use as a potential drug delivery biomaterial was examined for the first time. The results demonstrate that sponge-derived chitin scaffolds, impregnated with decamethoxine, effectively inhibit growth of the human pathogen Staphylococcus aureus in an agar diffusion assay.

Characterization and prediction of positional 4-hydroxyproline and sulfotyrosine, two post-translational modifications that can occur at substantial levels in CHO cells-expressed biotherapeutics

Biotherapeutics may contain a multitude of different post-translational modifications (PTMs) that need to be assessed and possibly monitored and controlled to ensure reproducible product quality. During early development of biotherapeutics, unexpected PTMs might be prevented by in silico identification and characterization together with further molecular engineering. Mass determinations of a human IgG1 (mAb1) and a bispecific IgG-ligand fusion protein (BsAbA) demonstrated the presence of unusual PTMs resulting in major +80 Da, and +16/+32 Da chain variants, respectively. For mAb1, analytical cation exchange chromatography demonstrated the presence of an acidic peak accounting for 20%. A + 79.957 Da modification was localized within the light chain complementarity-determining region-2 and identified as a sulfation based on accurate mass, isotopic distribution, and a complete neutral loss reaction upon collision-induced dissociation. Top-down ultrahigh resolution MALDI-ISD FT-ICR MS of modified and unmodified Fabs allowed the allocation of the sulfation to a specific Tyr residue. An aspartate in amino-terminal position-3 relative to the affected Tyr was found to play a key role in determining the sulfation. For BsAbA, a + 15.995 Da modification was observed and localized to three specific Pro residues explaining the +16 Da chain A, and +16 Da and +32 Da chain B variants. The BsAbA modifications were verified as 4-hydroxyproline and not 3-hydroxyproline in a tryptic peptide map via co-chromatography with synthetic peptides containing the two isomeric forms. Finally, our approach for an alert system based on in-house in silico predictors is presented. This system is designed to prevent these PTMs by molecular design and engineering during early biotherapeutic development.

Dehydroabietylamine Ureas and Thioureas as Tyrosyl-DNA Phosphodiesterase 1 Inhibitors That Enhance the Antitumor Effect of Temozolomide on Glioblastoma Cells

A new class of tyrosyl-DNA phosphodiesterase 1 (TDP1) inhibitors was found among resin acid derivatives. Several novel ureas and thioureas derived from dehydroabietylamine were synthesized and tested for TDP1 inhibition. The synthesized compounds showed IC₅₀ values in the range of 0.1 to 3.7 μM and demonstrated low cytotoxicity against the human tumor cell lines U-937, U-87MG, MDA-MB, SK-Mel8, A-549, MCF7, T98G, and SNB19. Several compounds showed enhancement of the cytotoxic activity of the alkylating agent temozolomide, which is used as a first line therapy against glioblastoma (GBM), in the GBM cell lines U-87MG and SNB19.

Protein Dynamics Preceding Photoisomerization of the Retinal Chromophore in Bacteriorhodopsin Revealed by Deep-UV Femtosecond Stimulated Raman Spectroscopy

Bacteriorhodopsin is a prototypical photoreceptor protein that functions as a light-driven proton pump. The retinal chromophore of bacteriorhodopsin undergoes C₁₃═C₁₄ trans-to-cis isomerization upon photoexcitation, and it has been believed to be the first event that triggers the cascaded structural changes in bacteriorhodopsin. We investigated the protein dynamics of bacteriorhodopsin using deep-ultraviolet resonance femtosecond stimulated Raman spectroscopy. It was found that the stimulated Raman signals of tryptophan and tyrosine residues exhibit significant changes within 0.2 ps after photoexcitation while they do not noticeably change during the isomerization process. This result implies that the protein environment changes first, and its change is small during isomerization. The obtained femtosecond stimulated Raman data indicate that ultrafast change is induced in the protein part by the sudden creation of the large dipole of the excited-state chromophore, providing an environment that realizes efficient and selective isomerization.

Conformational and Dynamical Effects of Tyr32 Phosphorylation in K-Ras: Molecular Dynamics Simulation and Markov State Models Analysis

Phosphorylation of tyrosine 32 in K-Ras has been shown to influence function by disrupting the GTPase cycle. To shed light on the underlying mechanism and atomic basis of this process, we carried out a comparative investigation of the oncogenic G12D K-Ras mutant and its phosphorylated variant (pTyr32) using all-atom molecular dynamics simulations and Markov state models. We show that, despite sharing a number of common features, G12D and pTyr32-G12D K-Ras exhibit some distinct conformational states and fluctuations. In addition to notable differences in conformation and dynamics of residues surrounding the GTP binding site, nonlocal changes were observed at a number of loops. Switch I is more flexible in pTyr32-G12D K-Ras while switch II is more flexible in G12D K-Ras. We also used time-lagged independent component analysis and k-means clustering to identify five metastable states for each system. We utilized transition path theory to calculate the transition probabilities for each state to build a Markov state model for each system. These models and other close inspections suggest that the phosphorylation of Tyr32 strongly affects protein dynamics and the active site conformation, especially with regards to the canonical switch conformations and dynamics.

Structures of single-layer β-sheet proteins evolved from β-hairpin repeats

Free-standing single-layer β-sheets are extremely rare in naturally occurring proteins, even though β-sheet motifs are ubiquitous. Here we report the crystal structures of three homologous, single-layer, anti-parallel β-sheet proteins, comprised of three or four twisted β-hairpin repeats. The structures reveal that, in addition to the hydrogen bond network characteristic of β-sheets, additional hydrophobic interactions mediated by small clusters of residues adjacent to the turns likely play a significant role in the structural stability and compensate for the lack of a compact hydrophobic core. These structures enabled identification of a family of secreted proteins that are broadly distributed in bacteria from the human gut microbiome and are putatively involved in the metabolism of complex carbohydrates. A conserved surface patch, rich in solvent-exposed tyrosine residues, was identified on the concave surface of the β-sheet. These new modular single-layer β-sheet proteins may serve as a new model system for studying folding and design of β-rich proteins.

Silk Hydrogels Crosslinked by the Fenton Reaction

Here, the Fenton reaction is used to prepare silk hydrogels through oxidation of tyrosine residues in silk fibroin, leading to dityrosine crosslinking. At pH 5.7, gelation occurs rapidly within 30 s, and the resultant opaque gels show soft properties with a storage modulus of ≈100 Pa. The addition of ascorbic acid to the Fenton reaction increases the dityrosine bonds in the hydrogels but has little effect on the rheological or mechanical properties. The results indicate that Fe(III) ions significantly interacted with silk fibroin during the Fenton reaction, most likely binding to sites such as tyrosine, glutamate, and aspartate residues, triggering the formation of β-sheet structures that may impede dityrosine bond formation due to steric hindrance. The use of an iron chelator or the operation of the Fenton reaction at pH 9.2 enables control over the interaction of Fe(III) ions with silk fibroin, achieving a hydrogel with improved optical properties and enhanced dityrosine bond formation. Hydrogels prepared by the Fenton reaction are cytocompatible as L929 mouse fibroblasts remain viable and are proliferative when seeded on the hydrogels. The results offer a useful approach to generate chemically crosslinked silk fibroin hydrogels without the use of enzyme-catalyzed reactions for biomedical applications.

Methionine and Selenomethionine as Energy Transfer Acceptors for Biomolecular Structure Elucidation in the Gas Phase

Mass spectrometry affords rapid and sensitive analysis of peptides and proteins. Coupling spectroscopy with mass spectrometry allows for the development of new methods to enhance biomolecular structure determination. Herein, we demonstrate two new energy acceptors that can be utilized for action-excitation energy transfer experiments. In the first system, C-S bonds in methionine act as energy acceptors from native chromophores, including tyrosine, tryptophan, and phenylalanine. Comparison among chromophores reveals that tyrosine transfers energy most efficiently at 266 nm, but phenylalanine and tryptophan also transfer energy with comparable efficiencies. Overall, the C-S bond dissociation yields following energy transfer are low for methionine, which led to an investigation of selenomethionine, a common analog that is found in many naturally occurring proteins. Sulfur and selenium are chemically similar, but C-Se bonds are weaker than C-S bonds and have lower lying σ* anti-bonding orbitals. Excitation of peptides containing tyrosine and tryptophan results in efficient energy transfer to selenomethionine and abundant C-Se bond dissociation. A series of helical peptides were examined where the positions of the donor or acceptor were systematically scanned to explore the influence of distance and helix orientation on energy transfer. The distance was found to be the primary factor affecting energy transfer efficiency, suggesting that selenomethionine may be a useful acceptor for probing protein structure in the gas phase.

Spatial Learning and Memory Impairment in Growing Mice Induced by Major Oxidized Tyrosine Product Dityrosine

This study focused on the effects of oxidized tyrosine products (OTPs) and major component dityrosine (DT) on the brain and behavior of growing mice. Male and female mice were treated with daily intragastric administration of either tyrosine (Tyr; 420 μg/kg body weight), DT (420 μg/kg body weight), or OTPs (1909 μg/kg body weight) for 35 days. We found that pure DT and OTPs caused redox state imbalance, elevated levels of inflammatory factors, hippocampal oxidative damage, and neurotransmitter disorders while activating the mitochondrial apoptosis pathway in the hippocampus and downregulating the genes associated with learning and memory. These events eventually led to growing mice learning and memory impairment, lagging responses, and anxiety-like behaviors. Furthermore, the male mice exhibited slightly more oxidative damage than the females. These findings imply that contemporary diets and food-processing strategies of the modern world should be modified to reduce oxidized protein intake.

Hydrogen Donation but not Abstraction by a Tyrosine (Y68) during Endoperoxide Installation by Verruculogen Synthase (FtmOx1)

Hydrogen-atom transfer (HAT) from a substrate carbon to an iron(IV)-oxo (ferryl) intermediate initiates a diverse array of enzymatic transformations. For outcomes other than hydroxylation, coupling of the resultant carbon radical and hydroxo ligand (oxygen rebound) must generally be averted. A recent study of FtmOx1, a fungal iron(II)- and 2-(oxo)glutarate-dependent oxygenase that installs the endoperoxide of verruculogen by adding O2 between carbons 21 and 27 of fumitremorgin B, posited that tyrosine (Tyr or Y) 224 serves as HAT intermediary to separate the C21 radical (C21•) and Fe(III)-OH HAT products and prevent rebound. Our reinvestigation of the FtmOx1 mechanism revealed, instead, direct HAT from C21 to the ferryl complex and surprisingly competitive rebound. The C21-hydroxylated (rebound) product, which undergoes deprenylation, predominates when low [O2] slows C21•-O2 coupling in the next step of the endoperoxidation pathway. This pathway culminates with addition of the C21-O-O• peroxyl adduct to olefinic C27 followed by HAT to the C26• from a Tyr. The last step results in sequential accumulation of Tyr radicals, which are suppressed without detriment to turnover by inclusion of the reductant, ascorbate. Replacement of each of four candidates for the proximal C26 H• donor (including Y224) with phenylalanine (F) revealed that only the Y68F variant (i) fails to accumulate the first Tyr• and (ii) makes an altered major product, identifying Y68 as the donor. The implied proximities of C21 to the iron cofactor and C26 to Y68 support a new docking model of the enzyme-substrate complex that is consistent with all available data.

Tyrosinase inhibitory study of flavonolignans from the seeds of Silybum marianum (Milk thistle)

Anti-melanogenesis effects of silymarin from milk thistle have been reported recently, but detailed tyrosinase inhibition properties of individual components have not been investigated. This study purported to substantiate tyrosinase inhibition and its mechanism based on a single metabolite. The responsible components for tyrosinase inhibition of target source were found out as flavonolignans which consist of isosilybin A (1), isosilybin B (2), silydianin (3), 2,3-dihydrosilychristin (4), silychristin A (5), silychristin B (6) and silybin (7), respectively. The isolated flavonolignans (1-7) inhibited both monophenolase (IC50 = 1.7-7.6 µM) and diphenolase (IC50 = 12.1-44.9 µM) of tyrosinase significantly. Their inhibitions were 10-fold effective in comparison with their mother skeletons (8-10). Inhibitory functions were also proved by HPLC analysis using N-acetyl-l-tyrosine as substrate. The predominant formation of Emet·I was confirmed from a long prolongation of lag time and a decrease of the static state activity of the enzyme. All tested compounds had a significant binding affinity to tyrosinase with KSV values of 0.06-0.27 × 104 L·mol-1, which are well correlated with IC50s. In kinetic study, all flavonolignan (1-7) were mixed type I (KI < KIS) inhibitors, whereas their mother skeletons (8-10) were competitive ones. The UPLC-ESI-TOF/MS analysis showed that the isolated inhibitors are the most abundant metabolites in the target plant.

Synthesis and Preliminary Biological Evaluation of Two Fluoroolefin Analogs of Largazole Inspired by the Structural Similarity of the Side Chain Unit in Psammaplin A

Largazole, isolated from a marine Cyanobacterium of the genus Symploca, is a potent and selective Class I HDAC (histone deacetylation enzymes) inhibitor. This natural 16-membered macrocyclic depsipeptide features an interesting side chain unit, namely 3-hydroxy-7-mercaptohept-4-enoic acid, which occurs in many other natural sulfur-containing HDAC inhibitors. Notably, one similar fragment, where the amide moiety replaces the trans alkene moiety, appears in Psammaplin A, another marine natural product with potent HDAC inhibitory activities. Inspired by such a structural similarity, we hypothesized the fluoroolefin moiety would mimic both the alkene moiety in Largazole and the amide moiety in Psammaplin A, and thus designed and synthesized two novel fluoro olefin analogs of Largazole. The preliminary biological assays showed that the fluoro analogs possessed comparable Class I HDAC inhibitory effects, indicating that this kind of modification on the side chain of Largazole was tolerable.

Halogenated Tyrosine Derivatives from the Tropical Eastern Pacific Zoantharians Antipathozoanthus hickmani and Parazoanthus darwini

In the search for bioactive marine natural products from zoantharians of the Tropical Eastern Pacific, four new tyrosine dipeptides, named valdiviamides A-D (1-4), were isolated from Antipathozoanthus hickmani, and two new tyramine derivatives, 5 and 6, from Parazoanthus darwini. The phenols of all six tyrosine derivatives are substituted by bromine and/or iodine atoms at the ortho positions of the hydroxyl. The planar structures of these aromatic alkaloids were elucidated from 1D and 2D NMR experiments in combination with HRESIMS data, and the absolute configurations of 1-4 were deduced from comparison between experimental and calculated electronic circular dichroism spectra. As halogenated tyrosine derivatives could represent chemotaxonomic markers of these genera, we decided to undertake the first chemical investigation of another species, Terrazoanthus cf. patagonichus. As expected, no halogenated metabolite was evidenced in the species, but we report herein the identification of two new zoanthoxanthin derivatives, named zoamides E (7) and F (8), from this species. Antimicrobial and cytotoxicity bioassays revealed that valdiviamide B (2) displayed moderate cytotoxicity against the HepG2 cell line with an IC₅₀ value of 7.8 μM.

Tyrosines involved in the activity of φ29 single-stranded DNA binding protein

The genome of Bacillus subtilis phage ϕ29 consists of a linear double-stranded DNA with a terminal protein (TP) covalently linked to each 5’ end (TP-DNA). ϕ29 DNA polymerase is the enzyme responsible for viral DNA replication, due to its distinctive properties: high processivity and strand displacement capacity, being able to replicate the entire genome without requiring the assistance of processivity or unwinding factors, unlike most replicases. ϕ29 single-stranded DNA binding protein (SSB) is encoded by the viral gene 5 and binds the ssDNA generated in the replication of the ϕ29 TP-DNA. It has been described to stimulate the DNA elongation rate during the DNA replication. Previous studies proposed residues Tyr50, Tyr57 and Tyr76 as ligands of ssDNA. The role of two of these residues has been determined in this work by site-directed mutagenesis. Our results showed that mutant derivative Y57A was unable to bind to ssDNA, to stimulate the DNA elongation and to displace oligonucleotides annealed to M13 ssDNA, whereas mutant Y50A behaved like the wild-type SSB.

Evidence of a Thermodynamic Ramp for Hole Hopping to Protect a Redox Enzyme from Oxidative Damage

Redox proteins and enzymes are at risk of irreversible oxidative damage from highly oxidizing intermediates generated in the active site in the case of unsuccessful functional reaction. Chains of tyrosine and/or tryptophan residues have been recently proposed to provide protection to the active site and the whole protein by delivering oxidizing equivalents (holes) out of the protein via a multistep hopping mechanism. In the present work we use a hybrid quantum/classical theoretical-computational methodology based on the perturbed matrix method and on molecular dynamics simulations to calculate the oxidation potential difference along a chain of tyrosine and tryptophan residues in a human redox enzyme of major importance, a superoxide dismutase, which acts as antioxidant defense. We show that the hole hopping is thermodynamically favored along such a chain and that the hopping propensity is strongly affected by the protein environment and in particular by the active site and its second coordination sphere.

Engineering tyrosine residues into hemoglobin enhances heme reduction, decreases oxidative stress and increases vascular retention of a hemoglobin based blood substitute

Hemoglobin (Hb)-based oxygen carriers (HBOC) are modified extracellular proteins, designed to replace or augment the oxygen-carrying capacity of erythrocytes. However, clinical results have generally been disappointing due to adverse side effects, in part linked to the intrinsic oxidative toxicity of Hb. Previously a redox-active tyrosine residue was engineered into the Hb β subunit (βF41Y) to facilitate electron transfer between endogenous antioxidants such as ascorbate and the oxidative ferryl heme species, converting the highly oxidizing ferryl species into the less reactive ferric (met) form. We inserted different single tyrosine mutations into the α and β subunits of Hb to determine if this effect of βF41Y was unique. Every mutation that was inserted within electron transfer range of the protein surface and the heme increased the rate of ferryl reduction. However, surprisingly, three of the mutations (βT84Y, αL91Y and βF85Y) also increased the rate of ascorbate reduction of ferric(met) Hb to ferrous(oxy) Hb. The rate enhancement was most evident at ascorbate concentrations equivalent to that found in plasma (< 100 μM), suggesting that it might be of benefit in decreasing oxidative stress in vivo. The most promising mutant (βT84Y) was stable with no increase in autoxidation or heme loss. A decrease in membrane damage following Hb addition to HEK cells correlated with the ability of βT84Y to maintain the protein in its oxygenated form. When PEGylated and injected into mice, βT84Y was shown to have an increased vascular half time compared to wild type PEGylated Hb. βT84Y represents a new class of mutations with the ability to enhance reduction of both ferryl and ferric Hb, and thus has potential to decrease adverse side effects as one component of a final HBOC product.

Site-specific observation of the conformational change of a protein with 15N-labeled Tyr residues using NMR

One of the reasons it is difficult to analyze protein structural dynamics at atomic resolution using NMR is the molecular size of the protein. The selective amino acid labeling method is one of the effective methods that can solve this problem. In this study, to determine the site-specific conformational change in 3α-hydroxysteroid dehydrogenase from Pseudomonas sp. B-0831 (Ps3αHSD), which forms a dimer composed of two 26 kDa subunits, we expressed and purified ¹⁵N-Tyr labeled Ps3αHSD and its mutants, and analyzed the conformational change upon NADH binding. Using the Tyr substituted mutants, we first assigned the respective signals of four Tyr residues. In the titration experiments with NADH, the four Tyr signals changed uniquely; changes in chemical shift and signal broadening were observed. The NADH binding affinity, determined from the plots of the ¹H and ¹⁵N chemical shift changes, was comparable to those reported previously. Together with the crystal structure information for Ps3αHSD in the NADH-free and -bound states, site-specific conformational changes including environmental changes could be deduced.

Metabolic engineering of microorganisms for production of aromatic compounds

Metabolic engineering has been enabling development of high performance microbial strains for the efficient production of natural and non-natural compounds from renewable non-food biomass. Even though microbial production of various chemicals has successfully been conducted and commercialized, there are still numerous chemicals and materials that await their efficient bio-based production. Aromatic chemicals, which are typically derived from benzene, toluene and xylene in petroleum industry, have been used in large amounts in various industries. Over the last three decades, many metabolically engineered microorganisms have been developed for the bio-based production of aromatic chemicals, many of which are derived from aromatic amino acid pathways. This review highlights the latest metabolic engineering strategies and tools applied to the biosynthesis of aromatic chemicals, many derived from shikimate and aromatic amino acids, including L-phenylalanine, L-tyrosine and L-tryptophan. It is expected that more and more engineered microorganisms capable of efficiently producing aromatic chemicals will be developed toward their industrial-scale production from renewable biomass.

Express Method for Isolation of Ready-to-Use 3D Chitin Scaffolds from Aplysina archeri (Aplysineidae: Verongiida) Demosponge

Sponges are a valuable source of natural compounds and biomaterials for many biotechnological applications. Marine sponges belonging to the order Verongiida are known to contain both chitin and biologically active bromotyrosines. Aplysina archeri (Aplysineidae: Verongiida) is well known to contain bromotyrosines with relevant bioactivity against human and animal diseases. The aim of this study was to develop an express method for the production of naturally prefabricated 3D chitin and bromotyrosine-containing extracts simultaneously. This new method is based on microwave irradiation (MWI) together with stepwise treatment using 1% sodium hydroxide, 20% acetic acid, and 30% hydrogen peroxide. This approach, which takes up to 1 h, made it possible to isolate chitin from the tube-like skeleton of A. archeri and to demonstrate the presence of this biopolymer in this sponge for the first time. Additionally, this procedure does not deacetylate chitin to chitosan and enables the recovery of ready-to-use 3D chitin scaffolds without destruction of the unique tube-like fibrous interconnected structure of the isolated biomaterial. Furthermore, these mechanically stressed fibers still have the capacity for saturation with water, methylene blue dye, crude oil, and blood, which is necessary for the application of such renewable 3D chitinous centimeter-sized scaffolds in diverse technological and biomedical fields.

Gelatin-Based Hydrogels through Homobifunctional Triazolinediones Targeting Tyrosine Residues

Gelatin is a biopolymer with interesting properties that can be useful for biomaterial design for different applications such as drug delivery systems, or 3D scaffolds for tissue engineering. However, gelatin suffers from poor mechanical stability at physiological temperature, hence methods for improving its properties are highly desirable. In the present work, a new chemical cross-linking strategy based on triazolinedione ene-type chemistry towards stable hydrogel is proposed. Two different homobifunctional 1,2,4-triazoline-3,5(4H)-diones, namely 4,4'-hexane-1,6-diylbis(3H-1,2,4-triazoline-3,5(4H)-dione) 1 and 4,4'-[methylenebis(4,1-phenylene)]bis(3H-1,2,4-triazoline-3,5(4H)-dione) 2 were used as cross-linkers in different ratio to tyrosine residues in gelatin. The reaction was proved effective in all experimented conditions and hydrogels featured with different thermal stability were obtained. In general, the higher the cross-linker/tyrosine ratio, the more thermostable the hydrogel. The swelling properties are strictly dependent upon the chemical nature of the cross-linker.

Bacterial biofilm destruction by size/surface charge-adaptive micelles

Biofilms formed by pathogenic bacteria are one of the most important reasons for multidrug resistance. One of the major limitations in the biofilm treatment is the existence of intensive matrices, which greatly block the diffusion of antimicrobial agents. In the current study, we designed poly(aspartamide)-derived micelles self-assembled from cationic copolymers with azithromycin-conjugated and pH-sensitive copolymers, followed by loading cis-aconityl-d-tyrosine (CA-Tyr) via electrostatic interactions. In response to the acidic microenvironment of the biofilm matrix, the hydrophilic transition of the pH-sensitive copolymers and the removal of CA-Tyr led to a sharp decrease in micelle size from 107 nm to 54 nm and a rapid shift in their zeta potential from -11.7 mV to +26.4 mV, which facilitated the penetration of the micelles into biofilms. The acid-labile release of d-tyrosine disintegrated the biofilm matrix, and the lipase-triggered release of azithromycin eradicated the bacteria in the biofilms. An in vitro test was performed on pre-established P. aeruginosa biofilms in microwells, while biofilms grown on catheters were surgically implanted in rats for in vivo evaluation. The results demonstrated the capabilities of the size/surface charge-adaptive micelles in the intensive infiltration in the biofilm matrix and spatiotemporal release of biofilm dispersion and antibacterial agents for the comprehensive treatment of biofilm-relevant infections.

Inducible, Selective Labeling of Proteins via Enzymatic Oxidation of Tyrosine

Proteins can be labeled site-specifically and in inducible fashion by exposing a small peptide tag (G₄Y) on any of its termini and activating the newly exposed tyrosine residue with the enzyme mushroom tyrosinase. The enzyme generates a quinone by oxidizing the tyrosine, which in turn can perform strain-promoted oxidation-controlled ortho-quinone cycloaddition (SPOCQ) with strained alkynes and alkenes, generating a stable conjugation product. Here, we describe a protocol to perform SPOCQ reaction on proteins, along with notes to optimize yield and reaction rates. Conjugation efficiencies of over 95% to antibodies have been reported using this protocol.

Structure and function of the insulin receptor-a personal perspective

Immunoprecipitation with autoantibodies to the insulin receptor derived from patients with extreme insulin resistance and acanthosis nigricans revealed that the receptor is comprised of two subunits of 135 kDa (α subunit) and 95 kDa (β subunit) and that insulin induces the rapid phosphorylation of the β subunit in intact cells. Incubation of a highly purified insulin receptor preparation with [γ-³²P]ATP also resulted in tyrosine phosphorylation of the β subunit in an insulin-dependent manner, suggesting that the receptor itself is a tyrosine-specific protein kinase. Furthermore, a Japanese boy with insulin resistance and acanthosis nigricans was found to be heterozygous for a mutation of the insulin receptor gene that resulted in the replacement of glycine-996 with valine in the ATP binding site of the receptor. Expression of the mutant receptor in cultured cells revealed it to be deficient in tyrosine kinase activity and mediation of insulin action, suggesting that the tyrosine kinase activity of the insulin receptor is essential for insulin action in vivo.

Time-dependent mucoadhesion of conjugated bioadhesive polymers

The time-dependent bioadhesive performance of various polymers was evaluated using a texture analyzer apparatus and freshly excised rat small intestinal tissue. A series of novel bioadhesive polymers were prepared by conjugating L-phenylalanine, L-tyrosine, and L-DOPA to either a low molecular weight poly (butadiene-maleic anhydride) or a high molecular weight poly (ethylene-maleic anhydride). Bioadhesive force was characterized as a function of time relative to polycarbophil, a slightly cross-linked poly (acrylic acid)-derivative, revealing different fracture strengths and tensile work for each of the six backbone-side chain conjugations that were studied. While polycarbophil showed a rapid and significant loss of bioadhesion over the testing period, the newly developed synthetic polymers were able to maintain their bioadhesive performance over the course of 91 min with the overall magnitude of bioadhesion corresponding to the hydrogen bonding potential of the associated side chains. These results highlight the potential of these polymers for use in the development of more effective bioadhesive oral drug delivery systems.

The toxicity of coated silver nanoparticles to Daphnia carinata and trophic transfer from alga Raphidocelis subcapitata

Nanoparticles (NPs) are causing threats to the environment. Silver NPs (AgNPs) are increasingly used in commercial products and may end up in freshwater ecosystems. The freshwater organisms are vulnerable due to water-borne and dietary exposure to AgNPs. Surface properties play an important role in the fate and behavior of AgNPs in the aquatic environment and their effects on organisms. However, effects of surface properties of AgNPs on organisms are poorly understood. In this study, we explored the effects of AgNPs coated with three different ligands; Tyrosine (T-AgNP), Epigallocatechin gallate (E-AgNP) and Curcumin (C-AgNP) in relation to the toxicity to a key aquatic organism; Daphnia carinata. The study focused on how coatings determine fate of NPs in the medium, mortality, feeding behaviour, bioaccumulation and trophic transfer from the freshwater alga, Raphidocelis subcapitata to daphnids. NP stability tests indicated that T-AgNPs were least stable in the ASTM daphnia medium while C-AgNPs were most stable. 48 h EC50 values of AgNPs to D. carinata were in the order of E-AgNP (19.37 μg L-1) > C-AgNP (21.37 μg L-1) > T-AgNP (49.74 μg L-1) while the 48 h EC50 value of Ag+ ions was 1.21 μg L-1. AgNP contaminated algae significantly decreased the feeding rates of daphnids. However, no significant differences were observed in feeding rates between algae contaminated with differently coated AgNPs. Trophic transfer studies showed that AgNPs were transferred from algae to daphnids. The bioacumulation of AgNPs in algae and the diet-borne bioaccumulation of AgNPs in daphnids varied for differently coated AgNPs. Bioaccumulation of C-AgNPs in algae was 1.5 time higher than T-AgNPs. However, the accumulation of T-AgNPs in daphnids via trophic transfer was 2.6 times higher than T-AgNPs. The knowledge generated from this study enhances the understanding of surface property dependent toxicity, bioaccumulation and trophic transfer of AgNPs in aquatic environments.

UV Resonance Raman Spectroscopy as a Tool to Probe Membrane Protein Structure and Dynamics

Ultraviolet resonance Raman (UVRR) spectroscopy is a vibrational technique that reveals structures and dynamics of biological macromolecules without the use of extrinsic labels. By tuning the Raman excitation wavelength to the deep UV region (e.g., 228 nm), Raman signal from tryptophan and tyrosine residues are selectively enhanced, allowing for the study of these functionally relevant amino acids in lipid and aqueous environments. In this chapter, we present methods on the UVRR data acquisition and analysis of the tryptophan vibrational modes of a model β-barrel membrane protein, OmpA, in folded and unfolded conformations.

Discovery of High Affinity Receptors for Dityrosine through Inverse Virtual Screening and Docking and Molecular Dynamics

Dityrosine is the product of oxidation that has been linked to a number of serious pathological conditions. Evidence indicates that high amounts of dityrosine exist in oxidized milk powders and some milk related foodstuffs, further reducing the nutritional value of oxidized proteins. Therefore, we hypothesize that some receptors related to special diseases would be targets for dityrosine. However, the mechanisms of the interaction of dityrosine with probable targets are still unknown. In the present work, an inverse virtual screening approach was performed to screen possible novel targets for dityrosine. Molecular docking studies were performed on a panel of targets extracted from the potential drug target database (PDTD) to optimize and validate the screening results. Firstly, two different conformations cis- and trans- were found for dityrosine during minimization. Moreover, Tubulin (αT) (−11.0 kcal/mol) was identified as a target for cis-dityrosine (CDT), targets including αT (−11.2 kcal/mol) and thyroid hormone receptor beta-1 (−10.7 kcal/mol) presented high binding affinities for trans-dityrosine (TDT). Furthermore, in order to provide binding complexes with higher precision, the three docked systems were further refined by performing thermo dynamic simulations. A series of techniques for searching for the most stable binding pose and the calculation of binding free energy are elaborately provided in this work. The major interactions between these targets and dityrosine were hydrophobic, electrostatic and hydrogen bonding. The application of inverse virtual screening method may facilitate the prediction of unknown targets for known ligands, and direct future experimental assays.