14-3-3 interaction with phosphodiesterase 8A sustains PKA signaling and downregulates the MAPK pathway.

The cAMP/PKA and mitogen-activated protein kinase (MAPK) signaling cascade control many cellular processes and are highly regulated for optimal cellular responses upon external stimuli. Phosphodiesterase 8A (PDE8A) is an important regulator that inhibits signaling via cAMP-dependent PKA by hydrolyzing intracellular cAMP pool. Conversely, PDE8A activates the MAPK pathway by protecting CRAF/Raf1 kinase from PKA-mediated inhibitory phosphorylation at Ser259 residue, a binding site of scaffold protein 14-3-3. It still remains enigmatic as to how the cross-talk involving PDE8A regulation influences cAMP/PKA and MAPK signaling pathways. Here, we report that PDE8A interacts with 14-3-3ζ in both yeast and mammalian system, and this interaction is enhanced upon the activation of PKA, which phosphorylates PDE8A's Ser359 residue. Biophysical characterization of phospho-Ser359 peptide with 14-3-3ζ protein further supports their interaction. Strikingly, 14-3-3ζ reduces the catalytic activity of PDE8A, which upregulates the cAMP/PKA pathway while the MAPK pathway is downregulated. Moreover, 14-3-3ζ in complex with PDE8A and cAMP-bound regulatory subunit of PKA, RIα, delays the deactivation of PKA signaling. Our results define 14-3-3ζ as a molecular switch that operates signaling between cAMP/PKA and MAPK by associating with PDE8A.

Light and Cation-Driven Optical Switch based on a Stilbene-Appended Terpyridine System for the Design of Molecular-Scale Logic Devices.

A molecular system comprising a terpyridine moiety capable of coordinating with different cations and a photoswitchable stilbene unit has been utilized here for the fabrication of multiply configurable logic systems. Incorporation of a substituted stilbene unit into the terpyridine motif generates an intraligand charge-transfer-sensitive module whose absorption and emission spectral properties are highly sensitive to light as well as cations. On the basis of the optical response profile of the receptor in the presence of selected cations as well as light of a specific wavelength, we are able to demonstrate multiple Boolean logic functions such as INHIBIT, IMPLICATION, OR, NOR, and NAND, as well as various combinations of them. Of particular interest, we utilized the present system for the construction of security keypad locks and memory devices by maintaining a proper sequence of the stimuli and monitoring either absorption or emission spectral response at a specific wavelength as the output signal. In addition to various Boolean logic functions, the present system has also the ability to mimic fuzzy logic operations for generating an infinite-valued logic scheme depending on its emission spectral responses upon varying the concentration of cationic (Fe2+ and/or Zn2+) and anionic (CN-) inputs.

Low-cost photo-switches based on stilbene-appended Zn(II)-terpyridine complexes.

We report herein the synthesis, characterization, photophysics, and photo-isomerization behaviors of three Zn(II)-terpyridine complexes of the type [Zn(tpy-pvp-X)2]2+ (X = H, Me, and NO2) covalently tethered with stilbene moiety. The complexes exhibit absorption bands stretching up to the edge of the visible domain due to ligand → ligand charge transfer (LLCT) transitions and strong emission at room temperature in the visible due to radiative deactivation of 3LLCT state having lifetime within 1.0-3.0 ns. The stilbene motifs in the complexes undergo trans to cis isomerization upon irradiating with UV and visible light accompanied by significant alteration of their absorption, emission, and 1H NMR spectral profiles. Apart from the variation of electron donating and electron withdrawing substituent (X), the isomerization studies were also carried out in three different solvents (DCM, MeCN, and DMSO) to further tune their kinetic and thermodynamic parameters. The rate, rate constant and quantum yield of isomerization were estimated in all the solvents. The reverse process (cis to trans) also occurs very slowly on keeping but could be accelerated upon heating. Trans to cis photoisomerization leads to quenching of emission in case of 1 and 2, whereas backward thermal cis to trans conversion leads to restoration of emission. By contrast, for the nitro-derivative (3) forward process induces emission enhancement, while backward process gives rise to emission quenching. In essence, "on-off" and "off-on" emission switching is feasible for 1 and 2, whereas "off-on" and "on-off" emission switching occurs in case of 3. Emission spectral responses upon successive action of photonic and thermal input lead to the fabrication of INHIBIT and IMPLICATION logic gates. DFT and TD-DFT computational investigations were also undertaken to visualize their electronic structures, correct assignment of the spectral bands, and mode of isomerization process.

Targeting C-terminal Helical bundle of NCOVID19 Envelope (E) protein.

One of the most crucial characteristic traits of Envelope (E) proteins in the severe acute respiratory syndrome SARS-CoV-1 and NCOVID19 viruses is their membrane-associated oligomerization led ion channel activity, virion assembly, and replication. NMR spectroscopic structural studies of envelope proteins from both the SARS CoV-1/2 reveal that this protein assembles into a homopentamer. Proof of concept studies via truncation mutants on either transmembrane (VFLLV), glycosylation motif (CACCN), hydrophobic helical bundle (PVYVY) as well as replacing C-terminal "DLLV" segments or point mutants such as S68, E69 residues with cysteine have significantly reduced viral titers of SARS-CoV-1. In this present study, we have first developed SARS-2 E protein homology model based on the pentamer coordinates of SARS-CoV-1 E protein (86.4% structural identity) with good stereochemical quality. Next, we focused on the glycosylation motif and hydrophobic helical bundle regions of E protein shown to be important for viral replication. A four feature (4F) model comprising of an acceptor targeting S60 hydroxyl group, a donor feature anchoring the C40 residue, and two hydrophobic features anchoring the V47 L28, L31, Y55, and P51 residues formed the protein based pharmacophore model targeting the glycosylation motif and helical bundle of E protein. Database screening with this 4F protein pharmacophore, ADMET property filtering on enamine small molecule discovery collection yielded a focused library of ~7000 hits. Further molecular docking and visual inspection of docked pose interactions at the above mention V47 L28, L31, Y55, P51, S60, C40 residues led to the identification of 10 best hits. Our STD NMR binding assay results demonstrate that the ligand 3, 2-(2-amino-2-oxo-ethoxy)-N-benzyl-benzamide, binds to NCOVID19 E protein with a binding affinity (KD) of 141.7 ± 13.6 µM. Furthermore, the ligand 3 also showed binding to C-terminal peptide (NR25) as evidenced with the STD spectrums of wild type E protein would serve to confirm the involvement of C-terminal helical bundle as envisaged in this study.

Host-membrane interacting interface of the SARS coronavirus envelope protein: Immense functional potential of C-terminal domain.

The Envelope (E) protein in SARS Coronavirus (CoV) is a small structural protein, incorporated as part of the envelope. A major fraction of the protein has been known to be associated with the host membranes, particularly organelles related to intracellular trafficking, prompting CoV packaging and propagation. Studies have elucidated the central hydrophobic transmembrane domain of the E protein being responsible for much of the viroporin activity in favor of the virus. However, newer insights into the organizational principles at the membranous compartments within the host cells suggest further complexity of the system. The lesser hydrophobic Carboxylic-terminal of the protein harbors interesting amino acid sequences- suggesting at the prevalence of membrane-directed amyloidogenic properties that remains mostly elusive. These highly conserved segments indicate at several potential membrane-associated functional roles that can redefine our comprehensive understanding of the protein. This should prompt further studies in designing and characterizing of effective targeted therapeutic measures.

Investigating the inhibitory effects of entacapone on amyloid fibril formation of human lysozyme.

The misfolding of soluble protein to amyloid fibers or oligomers leads to cell membrane rupture, cell death, and a variety of amyloid-related diseases. Hence, inhibition of protein fibrillation is an important and promising method to prevent and treat these diseases. In this study, we have investigated the inhibitory effect of entacapone (Ent) on human lysozyme (HL) amyloid fibrillation using a combination of biophysical techniques; Rayleigh scattering (RLS) data indicated that Ent can reduce the aggregation of HL amyloid fibrillation with the inhibition constant (Λ) of (3.0 ± 0.5) × 103 M-1. This finding was further confirmed by thioflavin-T (ThT), 8-Anilino-1-naphthalenesulfonic acid (ANS) fluorescence assays and congo red (CR) binding absorption assays with an IC50 value of 125.89 ± 1.25 µM. Meanwhile, dynamic light scattering (DLS) showed that the size of HL amyloids decreases sharply after Ent treatment. This effect was positively correlated with Ent concentration. Atomic force microscopy (AFM) techniques confirmed that the formation of the fibril decreased significantly when HL was co-incubated with Ent. In addition, steady-state fluorescence spectra and synchronous fluorescence analysis suggested that the formation of stable complexes between Ent and HL contributes to maintain the alpha-helical structure of HL. The molecular docking study revealed that the Ent binds at the active pocket of HL with Glu35, Asp53, Gln58, Trp 64, Ala108 and Trp109 residues via hydrogen bonds, van-der-Waals forces and hydrophobic interactions. The epitope mapping of HL for its interaction with Ent was further elucidated using two-dimensional solution-state nuclear magnetic resonance (NMR) experiments. NMR results showed that the Trp64 and Trp109 of HL plays an important role for binding to Ent, correlating well with our docking result. Thus our study showed the potential of Ent to serve as an effective therapeutic agent for the therapy of amyloid-related diseases.

Stimuli-Responsive Near-Infrared Emissive Os(II)-Terpyridine Complexes with a Sense of Logic.

Two bis-tridentate Os(II) compounds based on a heteroditopic terpyridine-bipyridine-type ligand were synthesized, and their photophysical properties were thoroughly studied. The compounds exhibit strong spin-allowed 1MLCT bands in the visible domain (489-521 nm) as well as weak 1GS to 3MLCT bands within the 668-815 nm domain. The compounds display strong luminescence from the 3MLCT state in the near-infrared domain (728-780 nm) at room temperature having lifetimes in the range of 20.0-171.0 ns. After coordination of [Os(tpy-PhCH3/H2pbbzim)2]2+ unit to the terpyridine site of tpy-Hbzim-dipy, the complexes offer vacant pyridine-imidazole motifs for interacting with cationic and anionic guests. Consequently, photophysical properties of the compounds were tuned to a great extent upon interaction with selected cations, anions, pH, as well as protons. Anion-induced alteration of the ground- and excited-state properties of the compound lead to recognition of specific anions in solution. Significant change in the optical spectral behaviors as well as switching of emission spectral properties of the compounds was done in the NIR region upon treating with anions, cations, protons, and solvents (dichloromethane, acetonitrile, methanol, dimethylsulfoxide, and water). Moreover, the optical outputs in response to external stimuli were used to demonstrate binary functions of two-input IMPLICATION, NOR, and XNOR logic gates.

Enhanced Silkworm Cecropin B Antimicrobial Activity against Pseudomonas aeruginosa from Single Amino Acid Variation.

Pseudomonas aeruginosa is an opportunistic bacterial pathogen causing severe infections in hospitalized and immunosuppressed patients, particularly individuals affected by cystic fibrosis. Several clinically isolated P. aeruginosa strains were found to be resistant to three or more antimicrobial classes indicating the importance of identifying new antimicrobials active against this pathogen. Here, we characterized the antimicrobial activity and the action mechanisms against P. aeruginosa of two natural isoforms of the antimicrobial peptide cecropin B, both isolated from the silkworm Bombyx mori. These cecropin B isoforms differ in a single amino acid substitution within the active portion of the peptide, so that the glutamic acid of the E53 CecB variant is replaced by a glutamine in the Q53 CecB isoform. Both peptides showed a high antimicrobial and membranolytic activity against P. aeruginosa, with Q53 CecB displaying greater activity compared with the E53 CecB isoform. Biophysical analyses, live-cell NMR, and molecular-dynamic-simulation studies indicated that both peptides might act as membrane-interacting elements, which can disrupt outer-membrane organization, facilitating their translocation toward the inner membrane of the bacterial cell. Our data also suggest that the amino acid variation of the Q53 CecB isoform represents a critical factor in stabilizing the hydrophobic segment that interacts with the bacterial membrane, determining the highest antimicrobial activity of the whole peptide. Its high stability to pH and temperature variations, tolerance to high salt concentrations, and low toxicity against human cells make Q53 CecB a promising candidate in the development of CecB-derived compounds against P. aeruginosa.

Synthesis, Structural Characterization, and Luminescence Switching of Diarylethene-Conjugated Ru(II)-Terpyridine Complexes by trans-cis Photoisomerization: Experimental and DFT/TD-DFT Investigation.

We synthesized and thoroughly characterized a new family of diarylethene-conjugated mononuclear Ru(II)-terpyridine complexes and investigated in detail their photophysical, electrochemical, and spectroelectrochemical behaviors. Interestingly, the compounds show moderately strong room-temperature luminescence predominantly from their 3MLCT state with luminescence lifetime varying between 8.43 and 22.82 ns. Because of the presence of diarylethene unit, all the monometallic complexes underwent trans-to-cis photoisomerization upon interaction with UV light with substantial changes in their absorption and luminescence spectra. Reverting back from the cis to the trans form is also made possible upon treatment with visible light or by heat. Trans-to-cis isomerization leads to almost complete quenching of luminescence, while backward cis-to-trans isomerization gives rise to restoration of the original luminescence for all the complexes. Thus, "on-off" and "off-on" emission switching was made possible upon successive interaction of the complexes with UV and visible light. Computational investigation involving density functional theory (DFT) and time-dependent DFT methods was done for proper assignment of the experimental absorption and emission spectral bands in the complexes. Finally, experimentally observed trend on the absorption and emission spectral behaviors of the complexes upon photoisomerization was also compared with the calculated results.

Synthesis, Photophysics, and Switchable Luminescence Properties of a New Class of Ruthenium(II)-Terpyridine Complexes Containing Photoisomerizable Styrylbenzene Units.

We report here the synthesis and structural characterization of a new class of homoleptic terpyridine complexes of Ru(II) containing styrylbenzene moieties to improve room-temperature luminescence properties. Solid-state structure determination of 2 was done through single-crystal X-ray diffraction. Tuning of photophysical properties was done by incorporating both electron-donating and electron-withdrawing substituents in the ligand. The complexes exhibit strong emission having lifetimes in the range of 10.0-158.5 ns, dependent on the substituent and the solvent. Good correlations were also observed between Hammett σp parameters with the lifetimes of the complexes. Styrylbenzene moieties in the complexes induce trans-trans to trans-cis isomerization accompanied by huge alteration of their spectral profiles upon treating with UV light. Reversal of trans-cis to trans-trans forms was also achieved on interacting with visible light. Change from trans-trans to the corresponding trans-cis form leads to emission quenching, whereas trans-cis to the corresponding trans-trans form leads to restoration of emission. In essence, "on-off" and "off-on" photoswitching of luminescence was observed. Calculations involving density functional theory (DFT) and time-dependent-DFT methods were performed to understand the electronic structures as well as for appropriate assignment of the absorption and emission bands.

Accelerated molecular dynamics simulation analysis of MSI-594 in a lipid bilayer.

Multidrug resistance against the existing antibiotics is one of the most challenging threats across the globe. Antimicrobial peptides (AMPs), in this regard, are considered to be one of the effective alternatives that can overcome bacterial resistance. MSI-594, a 24-residue linear alpha-helical cationic AMP, has been shown to function via the carpet mechanism to disrupt bacterial membrane systems. To better understand the role of lipid composition in the function of MSI-594, in the present study, eight different model membrane systems have been studied using accelerated molecular dynamics (aMD) simulations. The simulated results are helpful in discriminating the particular effects of cationic MSI-594 against zwitterionic POPC, anionic POPG and POPS, and neutral POPE lipid moieties. Additionally, the effects of various heterogeneous POPC/POPG (7 : 3), POPC/POPS (7 : 3), and POPG/POPE (1 : 3 and 3 : 1) bilayer systems on the dynamic interaction of MSI-594 have also been investigated. The effect on the lipid bilayer due to the interaction with the peptide is characterized by lipid acyl-chain order, membrane thickness, and acyl-chain dynamics. Our simulation results show that the lipid composition affects the membrane interaction of MSI-594, suggesting that membrane selectivity is crucial to its mechanism of action. The results reported in this study are helpful to obtain accurate atomistic-level information governing MSI-594 and its membrane disruptive antimicrobial mechanism of action, and to design next generation potent antimicrobial peptides.

Design of Ru(II) Complexes Based on Anthraimidazoledione-Functionalized Terpyridine Ligand for Improvement of Room-Temperature Luminescence Characteristics and Recognition of Selective Anions: Experimental and DFT/TD-DFT Study.

In this work we report synthesis and characterization of three rigid and linear rodlike monometallic Ru(II) complexes based on a terpyridine ligand tightly connected to 9,10-anthraquinone electron-acceptor unit through phenyl-imidazole spacer. The motivation of designing these complexes is to enhance their excited-state lifetimes at room temperature. Interestingly it is found that all three complexes exhibit luminescence at room temperature with excited-state lifetimes in the range of 1.6-52.8 ns, depending upon the coligand as well as the solvent. Temperature-dependent luminescence investigations indicate that the energy gap between the emitting 3MLCT state and nonemitting metal-centered state 3MC in the complexes increased enormously compared with parent [Ru(tpy)2]2+. In addition, by taking advantage of the imidazole NH proton(s), which became appreciably acidic upon combined effect of electron accepting anthraquinone moiety as well as metal ion coordination, we also examined anion recognition and sensing behaviors of the complexes in organic, mixed aqueous-organic as well as in solid medium through different optical channels such as absorption, steady-state and time-resolved emission, and 1H NMR spectroscopic techniques. In conjunction with the experiment, computational investigation was also employed to examine the electronic structures of the complexes and accurate assignment of experimentally observed spectral and redox behaviors.