Aggregation of cation-anionic and related polymethine dyes

Absorption, fluorescence, and fluorescence excitation spectra were studied for a number of cation-anionic and related anionic polymethine dyes in weakly polarand nonpolarsolvents, as well as in binary mixtures of solvents of different polarity. For some dyes, aggregation is observed in toluene or acetonitrile-toluene mixtures with low amounts of acetonitrile, which is revealed as appearance of new absorption bands and/or broadening of the initial bands of a monomeric dye. Solvent mixtures butyronitrilehexane with low butyronitrile content were found to greatly stimulate the formation of dye aggregates for most of the dyes studied. The absorption spectra of the aggregates are often blue-shifted with respect to the corresponding absorption spectra of parent monomeric dyes and/or represent broad continuums located both in the blue and red regions. For one of the cation-anionic dyes studied, which consists of 3,3′-diethylthiamonomethinecyanine cation and trimethinebenzoxanine anion, fluorescent aggregates were observed; their broad fluorescence band is located in the long-wavelength region. For this dye, gradual transition from nonfluorescent aggregates to fluorescent ones and then to monomeric ion pairs and dissociated ions was observed in butyronitrile-hexane mixtures with growing butyronitrile content

IL GIOCO MOLECOLARE TRA DRUG DISCOVERY E CHEMICAL BIOLOGY

La chemical biology \ue8 una disciplina vicina alla chimica farmaceutica strettamente connessa al processo di drug discovery mediante uno scambio di ruolo di inibitori/ligandi e probe molecolari. In tre esempi di applicazione della chemical biology-drug discovery vengono illustrati i linker per la bioconiugazione, le sonde fluorescenti in studi di interazione farmacorecettore cellulare (target engagement) e l\u2019indagine proteomica dei meccanismi biologici d\u2019azione di inibitori specifici

Designing selective Cys-ligands to unpair the binding of the Human Transcription Enhancer Associated Domain 4 (hTEAD-4) with its modulators to halt cancer cell growth

The Hippo Signalling cascade is an emerging target in tumour suppression regulation, neoplastic hypertrophy, and regenerative medicine. The pathway is activated by circulating anti-proliferative signals which leads to the phosphorylation of Yes Associated Protein (hYAP1) on Ser127/381, thus 14-3-3\u3c3 mediated cytosolic retention. Genetic alterations or exogenous factor may cause YAP nuclear migration and association to TEAD1-4 (Transcription Enhancer Associated Domain), triggering up-regulation of anti-apoptotic genes [1]. hTEAD is an enhancer that activates the nuclear transcription of genes as EMT\u2019s, EGFR and cyclins, and promotes the synthesis of survivin, tyrosine kinase HER3, and mitochondrial Bcl-xL involved in cell proliferation. TEAD binds a palmitic (palm) or myristic (myr) acids, tethered at Cys367 pocket, however its biological role is still not well known. hTEAD isoform-4 is the most represented of its family in solid tumours and its overexpression or mutation leads to cancer development and metastasis. Recent studies have considered hTEAD a promising target for anticancer drugs. Its inhibition strategy includes the disruption/prevention of YAP1:TEAD4 complex formation [2]. With the aim to develop a specific cysteine-directed inhibition strategy, we studied Cys on the protein surface and investigated their reactivity. Hence, our studies focus on characterizing the recombinant hTEAD4-ybd (aa217-434) surface though the analysis of the reactivity of its four Cys thiols (Cys310, Cys335, Cys367, Cys410), all close to YAP binding area. First, myr-Cys-367 was investigated to confirm the auto-myristoilation of the E. coli recombinant hTEAD4 through RP-chromatography on UHPLC-Orbitrap Q-Ex (ThermoFisher\u2122) by multicharged TIC deconvolution, and the total myr-TEAD was assessed around 25%. Myristate position was confirmed by FASP protein tryptic hydrolysis and tandem-MS peptide analysis. We studied hTEAD binding of a small disulphides and thiols library with different chemical properties through the exposed cysteines residues in presence of different concentration of reducing agent [3]. Top8 DDA (HCD)-MS/MS scan on the tryptic peptides suggested the ligands\u2019 high selectivity towards Cys335. Cys367 was never found conjugated, even in the non-Myr fraction, hinting the low accessibility to the lipid pocket. The number of surface reactive Cys was confirmed by a reverse-titration of the protein against increasing amount of thiophenol; excess of unreacted thiophenol was measured by HPLC-UV-ELSD (Agilent\u2122 1260), suggesting a 1:1 stoichiometry. We confirmed hTEAD-ybd ligand ratio by fluoresceine labelling with absorption and fluorescence differential spectroscopy. The ongoing work engages the screening of a larger compound library to study YAP:TEAD interaction with a ligand displacement assay of labelled TEAD to a rhodamine-tagged peptidomimetic probe to achieve structural information of the heterodimer interface and to start a hit-optimization programme. REFERENCES [1] Santucci M, Vignudelli T, et al. The Hippo Pathway and YAP/TAZ-TEAD Protein-Protein Interaction as Targets for Regenerative Medicine and Cancer Treatment. J Med Chem. 2015 Jun 25;58(12):4857-73. [2] Elisi G.M, Santucci M, et al. Repurposing of Drugs Targeting YAP-TEAD Functions. Cancers 2018, 10, 329. [3] Malpezzi G MSc Degree Thesis, Solvent exposure, and reactivity of the cysteines of Transcription Enhancer Associate Domain (TEAD), a potential anticancer target, 2021. University of Pavia \u2013 University of Modena and Reggio Emilia

Excitation-Energy Transfer Paths from Tryptophans to Coordinated Copper Ions in Engineered Azurins: a Source of Observables for Monitoring Protein Structural Changes

The intrinsic fluorescence of recombinant proteins offers a powerful tool to detect and characterize structural changes induced by chemical or biological stimuli. We show that metal-ion binding to a hexahistidine tail can significantly broaden the range of such structurally sensitive fluorescence observables. Bipositive metal-ions as Cu2+, Ni2+ and Zn2+ bind 6xHis-tag azurin and its 6xHis-tagged R129W and W48A-R129W mutants with good efficiency and, thereby, quench their intrinsic fluorescence. Due to a much more favourable spectral overlap, the 6xHis-tag/Cu2+ complex(es) are the most efficient quenchers of both W48 and W129 emissions. Based on simple F\uf6rster-type dependence of energy-transfer efficiency on donor/acceptor distance, we can trace several excitation-energy transfer paths across the protein structure. Unexpected lifetime components in the azurin 6xHis-tag/Cu2+ complex emission decays reveal underneath complexity in the conformational landscape of these systems. The new tryptophan emission quenching paths provide additional signals for detecting and identifying protein structural changes

Fluorometric detection of protein-ligand engagement: The case of phosphodiesterase5

Phosphodiesterases (PDEs) regulate the intracellular levels of cAMP and cGMP. The great clinical success of the PDE5 inhibitors, Sildenafil (Viagra), Vardenafil (Levitra) and Tadalafil (Cialis) has led to an increasing interest for this class of enzymes. Recent studies have shown a correlation between tumor growth and PDE5 overexpression, making PDE5-selective inhibitors promising candidates for cancer treatment. The search for such inhibitors rests today on radioactive assays. In this work, we exploit the conserved catalytic domain of the enzyme and propose a faster and safer method for detecting the binding of ligands and evaluate their affinities. The new approach takes advantage of Förster Resonance Energy Transfer (FRET) between, as the donor, a fluorescein-like diarsenical probe able to covalently bind a tetracysteine motif fused to the recombinant PDE5 catalytic domain and, as the acceptor, a rhodamine probe covalently bound to the pseudosubstrate cGMPS. The FRET efficiency decreases when a competitive ligand binds the PDE5 catalytic site and displaces the cGMPS-rhodamine conjugate. We have structurally investigated the PDE5/cGMPS-rhodamine complex by molecular modelling and have used the FRET signal to quantitatively characterize its binding equilibrium. Competitive displacement experiments were carried out with tadalafil and cGMPS. An adaptation of the competitive-displacement equilibrium model yielded the affinities for PDE5 of the incoming ligands, nano- and micromolar, respectively