Sterically hindered phenolic derivatives: effect on the production of Pseudomonas aeruginosa virulence factors, high-throughput virtual screening and ADME properties prediction.

Inhibition of quorum sensing is considered to be an effective strategy of control and treatment of a wide range of acute and persistent infections. Pseudomonas aeruginosa is an opportunistic bacterium with a high adaptation potential that contributes to healthcare-associated infections. In the present study, the effects of the synthesized hybrid structures bearing sterically hindered phenolic and heterocyclic moieties in a single scaffold on the production of virulence factors by P. aeruginosa were determined. It has been shown that the obtained compounds significantly reduce both pyocyanin and alginate production and stimulate the biosynthesis of siderophores in vitro, which may be attributed to their iron-chelating properties. The results of docking-based inverse high-throughput virtual screening indicate that transcription regulator LasR and Cu-transporter OPRC could be potential molecular targets for these compounds. Investigation of the impact small molecules exert on the molecular mechanisms of the production of bacterial virulence factors may pave the way for the design and development of novel antibacterial agents.

Stereodivergent Assembly of 2,6-cis- and -trans-Tetrahydropyrans via Base-Mediated Oxa-Michael Cyclization: The Key Role of the TMEDA Additive.

The stereodivergent synthesis of cis- and trans-2,6-disubstituted tetrahydropyrans (THPs) via sodium hexamethyldisilazide-promoted oxa-Michael cyclization of (E)-ζ-hydroxy α,ß-unsaturated esters is presented. The cyclization affords the kinetically favored trans-THPs with high stereoselectivity (dr up to 93:7) at a low temperature (-78 °C), while the room-temperature reaction does not produce the thermodynamically preferred cis-THPs as major products and occurs with poor stereocontrol. The addition of tetramethylethylenediamine (TMEDA) significantly improves the stereochemical outcome of the room-temperature cyclization and allows attaining high cis-selectivity (dr up to 99:1). The remarkable effect of TMEDA indicates that the sodium cation plays an important role in controlling the stereoselectivity of the thermodynamically driven process, that is, complexation of the cation with the cyclization products results in diminished selectivity. DFT calculations support this conclusion, indicating a greater difference in Gibbs energies of sodium-free cis- and trans-enolates compared to the respective sodium chelate complexes. The synthetic utility of the method has been demonstrated by the formal syntheses of (+)-Neopeltolide and (-)-Diospongin B and the total synthesis of (-)-Diospongin A.

Bismuth(III) Complexes with Schiff Bases: Synthesis, Characterization, Interaction with Biomolecules, Antioxidant and Antimicrobial Activity.

AIMS AND BACKGROUND: In contrast to antibiotics, metal complexes can realize more than one mechanism of biocidal action to fight multidrug-resistant bacterial strains (due essentially to the metal ions), involving targets like functional groups in the walls of microbial cells and various enzymes. Among the potential antimicrobials are Bi(III) complexes with diphenols. OBJECTIVE: The present work aimed at synthesizing and investigating novel Bi(III) complexes with Schiff bases as potential antimicrobial and antioxidant agents. METHODS: Bi(III) complexes were characterized by means of elemental analysis, FT-IR, UV-Vis, 1H NMR spectroscopy, XRD, cyclic voltammetry and conductivity measurements as well as biological methods. RESULTS: The complexes are characterized by the formula Bi(L)2Cl and pyramidal geometry of their coordination cores BiO2N2Cl, wherein the Bi(III) cation is coordinated by hydroxyl and azomethine moieties. The ligands coordinate in their monoanionic forms. The complexes are more lipophilic and more bioactive against the bacteria tested than the ligands. Both the ligands and their complexes exhibited the capability for the Fe(III)-Cyt c reduction and displayed comparable reducing rates. All the compounds are characterized by the DPPH and ABTS radical scavenging activity, and they are more active reductants than Trolox in the CUPRAC assay too. The peculiarities of the interaction of the complexes with BSA suggest that Cys-34 of BSA is not a major binding site for these complexes. According to molecular docking studies, the complexes bind to BSA via non-covalent interactions. CONCLUSION: Bi(III) complexation with Schiff bases plays an important role in their antimicrobial and antioxidant activities as well as in their interaction with BSA.

Silkworm carotenoprotein as an efficient carotenoid extractor, solubilizer and transporter.

Found in many organisms, water-soluble carotenoproteins are prospective antioxidant nanocarriers for biomedical applications. Yet, the toolkit of characterized carotenoproteins is rather limited: such proteins are either too specific binders of only few different carotenoids, or their ability to transfer carotenoids to various acceptor systems is unknown. Here, by focusing on a recently characterized recombinant ~27-kDa Carotenoid-Binding Protein from Bombyx mori (BmCBP) [Slonimskiy et al., International Journal of Biological Macromolecules 214 (2022): 664-671], we analyze its carotenoid-binding repertoire and potential as a carotenoid delivery module. We show that BmCBP forms productive complexes with both hydroxyl- and ketocarotenoids - lutein, zeaxanthin, astaxanthin, canthaxanthin and a smaller antioxidant, aporhodoxanthinone, but not with ß-carotene or retinal, which defines its broad ligand specificity toward xanthophylls valuable to human health. Moreover, the His-tagged BmCBP apoform is capable of cost-efficient and scalable enrichment of xanthophylls from various crude methanolic herbal extracts. Upon carotenoid binding, BmCBP remains monomeric and shows a remarkable ability to dynamically shuttle carotenoids to biological membrane models and to unrelated carotenoproteins, which in particular makes from the cyanobacterial Orange Carotenoid Protein a blue-light controlled photoswitch. Furthermore, administration of BmCBP loaded by zeaxanthin stimulates fibroblast growth, which is attractive for cell- and tissue-based assays.

Structural basis for the carotenoid binding and transport function of a START domain.

STARD3, a steroidogenic acute regulatory lipid transfer protein, was identified as a key xanthophyll-binding protein in the human retina. STARD3 and its homologs in invertebrates are known to bind and transport carotenoids, but this lacks structural elucidation. Here, we report high-resolution crystal structures of the apo- and zeaxanthin (ZEA)-bound carotenoid-binding protein from silkworm Bombyx mori (BmCBP). Having a STARD3-like fold, BmCBP features novel elements, including the Ω1-loop that, in the apoform, is uniquely fixed on the α4-helix by an R173-D279 salt bridge. We exploit absorbance, Raman and dichroism spectroscopy, and calorimetry to describe how ZEA and BmCBP mutually affect each other in the complex. We identify key carotenoid-binding residues, confirm their roles by ZEA-binding capacity and X-ray structures of BmCBP mutants, and also demonstrate that markedly different carotenoid-binding capacities of BmCBP and human STARD3 stem from differences in the structural organization of their carotenoid-binding cavity.

Analysis of Activity of Human Steroidogenic Acute Regulatory Protein (STARD1) Expressed in Escherichia coli Cells.

One of the main obstacles to the successful use of Escherichia coli cells for steroid transformation in biotechnological processes is inefficient transport of steroid substrates into the cells. Here, we tested the possibility of using human cholesterol transfer protein STARD1 (steroidogenic acute regulatory protein) to increase the efficiency of steroid uptake by bacterial cells. Genetic constructs were obtained for the synthesis in E. coli BL21 (DE3) cells of a truncated version of STARD1 containing protein functional domain (residues 66-285) and STARD1 (66-285)-GFP fusion protein, both carrying bacterial periplasmic targeting sequence pelB at the N-terminus. Analysis of preparations of E. coli/pET22b/STARD1-GFP cells by fluorimetry and Western blotting confirmed that the used expression system ensured the synthesis of the heterologous protein. Using fluorescence spectroscopy, it was demonstrated that the presence of STARD1 in the cells increased the efficiency of assimilation of NBD-labeled cholesterol analogues by E. coli/pET22b/STARD1 cells 1.3-1.6 times (p < 0.05) compared to the wild-type cells, thus demonstrating that human STARD1 exhibits its functional activity in bacterial cells. This opens prospects for optimizing and using a fundamentally new approach to increase the efficiency of steroid uptake by cells - the inclusion of a specific carrier protein in the cell membrane, which can expand the arsenal of methods used to obtain strains of microorganisms for synthesis.

A Hydrophobic Derivative of Ciprofloxacin as a New Photoinitiator of Two-Photon Polymerization: Synthesis and Usage for the Formation of Biocompatible Polylactide-Based 3D Scaffolds.

A hydrophobic derivative of ciprofloxacin, hexanoylated ciprofloxacin (CPF-hex), has been used as a photoinitiator (PI) for two-photon polymerization (2PP) for the first time. We present, here, the synthesis of CPF-hex and its application for 2PP of methacrylate-terminated star-shaped poly (D,L-lactide), as well a systematic study on the optical, physicochemical and mechanical properties of the photocurable resin and prepared three-dimensional scaffolds. CPF-hex exhibited good solubility in the photocurable resin, high absorption at the two-photon wavelength and a low fluorescence quantum yield = 0.079. Structuring tests showed a relatively broad processing window and revealed the efficiency of CPF-hex as a 2PP PI. The prepared three-dimensional scaffolds showed good thermal stability; thermal decomposition was observed only at 314 °C. In addition, they demonstrated an increase in Young's modulus after the UV post-curing (from 336 ± 79 MPa to 564 ± 183 MPa, which is close to those of a cancellous (trabecular) bone). Moreover, using CPF-hex as a 2PP PI did not compromise the scaffolds' low cytotoxicity, thus they are suitable for potential application in bone tissue regeneration.

New 20-hydroxycholesterol-like compounds with fluorescent NBD or alkyne labels: Synthesis, in silico interactions with proteins and uptake by yeast cells.

20-hydroxycholesterol is a signaling oxysterol with immunomodulating functions and, thus, structural analogues with reporter capabilities could be useful for studying and modulating the cellular processes concerned. We have synthesized three new 20-hydroxycholesterol-like pregn-5-en-3ß-ol derivatives with fluorescent 7-nitrobenzofurazan (NBD) or Raman-sensitive alkyne labels in their side-chains. In silico computations demonstrated the compounds possess good membrane permeability and can bind within active sites of known 20-hydroxycholesterol targets (e.g. Smoothened and yeast Osh4) and some other sterol-binding proteins (human LXRß and STARD1; yeast START-kins Lam4S2 and Lam2S2). Having found good predicted membrane permeability and binding to some yeast proteins, we tested the compounds on microorganisms. Fluorescent microscopy indicated the uptake of the steroids by both Saccharomyces cerevisiae and Yarrowia lipolytica, whereas only S. cerevisiae demonstrated conversion of the compounds into 3-O-acetates, likely because 3-O-acetyltransferase Atf2p is present only in its genome. The new compounds provide new options to study the uptake, intracellular distribution and metabolism of sterols in yeast cells as well as might be used as ligands for sterol-binding proteins.

Effect of the NBD-group position on interaction of fluorescently-labeled cholesterol analogues with human steroidogenic acute regulatory protein STARD1.

Steroidogenic acute regulatory protein (StAR, STARD1) is a key factor of intracellular cholesterol transfer to mitochondria, necessary for adrenal and gonadal steroidogenesis, and is an archetypal member of the START protein family. Despite the common overall structural fold, START members differ in their binding selectivity toward various lipid ligands, but the lack of direct structural information hinders complete understanding of the binding process and cholesterol orientation in the STARD1 complex in particular. Cholesterol binding has been widely studied by commercially available fluorescent steroids, but the effect of the fluorescent group position on binding remained underexplored. Here, we dissect STARD1 interaction with cholesterol-like steroids bearing 7-nitrobenz-2-oxa-1,3-diazol-4-yl (NBD) group in different positions, namely, with 22-NBD-cholesterol (22NC), 25-NBD-cholesterol (25NC), 20-((NBDamino)-pregn-5-en-3-ol (20NP) and 3-(NBDamino)-cholestane (3NC). While being able to stoichiometrically bind 22NC and 20NP with high fluorescence yield and quantitative exhaustion of fluorescence of some protein tryptophans, STARD1 binds 25NC and 3NC with much lower affinity and poor fluorescence response. In contrast to 3NC, binding of 20NP leads to STARD1 stabilization and substantially increases the NBD fluorescence lifetime. Remarkably, in terms of fluorescence response, 20NP slightly outperforms commonly used 22NC and can thus be used for screening of various potential ligands by a competition mechanism in the future.

High-yield soluble expression, purification and characterization of human steroidogenic acute regulatory protein (StAR) fused to a cleavable Maltose-Binding Protein (MBP).

Steroidogenic acute regulatory protein (StAR) is responsible for the rapid delivery of cholesterol to mitochondria where the lipid serves as a source for steroid hormones biosynthesis in adrenals and gonads. Despite many successful investigations, current understanding of the mechanism of StAR action is far from being completely clear. StAR was mostly obtained using denaturation/renaturation or in minor quantities in a soluble form at decreased temperatures that, presumably, limited the possibilities for its consequent detailed exploration. In our hands, existing StAR expression constructs could be bacterially expressed almost exclusively as insoluble forms, even upon decreased expression temperatures and in specific strains of Escherichia coli, and isolated protein tended to aggregate and was difficult to handle. To maximize the yield of soluble protein, optimized StAR sequence encompassing functional domain STARD1 (residues 66-285) was fused to the C-terminus of His-tagged Maltose-Binding Protein (MBP) with the possibility to cleave off the whole tag by 3C protease. The developed protocol of expression and purification comprising of a combination of subtractive immobilized metal affinity chromatography (IMAC) and size-exclusion chromatography allowed us to obtain up to 25 mg/1 L culture of completely soluble StAR protein, which was (i) homogenous according to SDS-PAGE, (ii) gave a single symmetrical peak on a gel-filtration, (iii) showed the characteristic CD spectrum and (iv) pH-dependent ability to bind a fluorescently-labeled cholesterol analogue. We conclude that our strategy provides fully soluble and native StAR protein which in future could be efficiently used for biotechnology and drug discovery aimed at modulation of steroids production.

Evaluation of the fluorescent probes Nile Red and 25-NBD-cholesterol as substrates for steroid-converting oxidoreductases using pure enzymes and microorganisms.

The fluorescent probes Nile Red (nonsteroidal dye) and 25-{N-[(7-nitrobenz-2-oxa-1,3-diazol-4-yl)-methyl]amino}-27-norcholesterol (25-NBD-cholesterol) (a cholesterol analog) were evaluated as novel substrates for steroid-converting oxidoreductases. Docking simulations with autodock showed that Nile Red fits well into the substrate-binding site of cytochrome P450 17α-hydroxylase/17,20-lyase (CYP17A1) (binding energy value of -8.3 kcal·mol⁻¹). Recombinant Saccharomyces cerevisiae and Yarrowia lipolytica, both expressing CYP17A1, were found to catalyze the conversion of Nile Red into two N-dealkylated derivatives. The conversion by the yeasts was shown to increase in the cases of coexpression of electron-donating partners of CYP17A1. The highest specific activity value (1.30 ± 0.02 min⁻¹) was achieved for the strain Y. lipolytica DC5, expressing CYP17A1 and the yeast's NADPH-cytochrome P450 reductase. The dye was also metabolized by pure CYP17A1 into the N-dealkylated derivatives, and gave a type I difference spectrum when titrated into low-spin CYP17A1. Analogously, docking simulations demonstrated that 25-NBD-cholesterol binds into the active site of the microbial cholesterol oxidase (CHOX) from Brevibacterium sterolicum (binding energy value of -5.6 kcal·mol⁻¹). The steroid was found to be converted into its 4-en-3-one derivative by CHOX (K(m) and k(cat) values were estimated to be 58.1 ± 5.9 µM and 0.66 ± 0.14 s⁻¹, respectively). The 4-en-3-one derivative was also detected as the product of 25-NBD-cholesterol oxidation with both pure microbial cholesterol dehydrogenase (CHDH) and a pathogenic bacterium, Pseudomonas aeruginosa, possessing CHOXs and CHDHs. These results provide novel opportunities for investigation of the structure-function relationships of the aforementioned oxidoreductases, which catalyze essential steps of steroid bioconversion in mammals (CYP17A1) and bacteria (CHOX and CHDH), with fluorescence-based techniques.

22-NBD-cholesterol as a novel fluorescent substrate for cholesterol-converting oxidoreductases.

Docking simulations and experimental data indicate that 22-(N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)-23,24-bisnor-5-cholen-3ß-ol (22-NBD-cholesterol), a common fluorescent sterol analog, binds into active sites of bovine cytochrome P450scc and microbial cholesterol dehydrogenases (CHDHs) and then undergoes regiospecific oxidations by these enzymes. The P450scc-dependent system was established to realize N-dealkylation activity toward 22-NBD-cholesterol, resulting in 7-nitrobenz[c][1,2,5]oxadiazole-4-amine (NBD-NH(2)) formation as a dominant fluorescent product. Basing on LC-MS data of the probes derivatized with hydroxylamine or cholesterol oxidase, both pregnenolone and 20-formyl-pregn-5-en-3ß-ol were deduced to be steroidal co-products of NBD-NH(2), indicating intricate character of the reaction. Products of CHDH-mediated conversions of 22-NBD-cholesterol were defined as 3-oxo-4-en and 3-oxo-5-en derivatives of the steroid. Moreover, the 3-oxo-4-en derivative was also found to be formed after 22-NBD-cholesterol incubation with pathogenic bacterium Pseudomonas aeruginosa, indicating a possible application of the reaction for a selective and sensitive detection of some microbes. The 3-keto-4-en derivative of 22-NBD-cholesterol may be also suitable as a new fluorescent probe for steroid hormone-binding enzymes or receptors.