Phanogracilins A-C, New Bibenzochromenones of Crinoid Phanogenia gracilis (Hartlaub, 1890)

Three new bibenzochromenones named phanogracilins A-C (1-3) were isolated from the crinoid Phanogenia gracilis. The structure of 1 was established using X-ray crystallography as 5,5',6,6',8,8'-hexahydroxy-2,2'-dipropyl-4H,4'H-[7,9'-bibenzo[g]chromene]-4,4'-dione. This allowed us to assign reliably 2D NMR signals for compound 1 and subsequently for its isomer 2 that differed in the connecting position of two benzochromenone moieties (7,10' instead of 7,9'), and compound for 3 that differed in the length of the aliphatic chain of one of the fragments. Compound 4 was derived from 1 in alkaline conditions, and its structure was elucidated as 5,5',6',8,8'-pentahydroxy-2,2'-dipropyl-4H,4'H-[7,9'-bibenzo[g]chromene]-4,4',6,9-tetraone. Even though compounds 1-4 did not contain stereo centers, they possessed notable optical activity due to sterical hindrances, which limited the internal rotation of two benzochromenone fragments around C(7)-C(9'/10') bonds. Isolated bibenzochromenones 1-4 were tested for their antiradical, neuroprotective and antimicrobial activities. Compounds 1, 3 and 4 demonstrated significant antiradical properties towards ABTS radicals higher than the positive control trolox. Compounds 1 and 4 exhibited moderate neuroprotective activity, increasing the viability of rotenone-treated Neuro-2a cells at a concentration of 1 µM by 9.8% and 11.8%, respectively. Compounds 1 and 3 at concentrations from 25 to 100 μM dose-dependently inhibited the growth of Gram-positive bacteria S. aureus and yeast-like fungi C. albicans, and they also prevented the formation of their biofilms. Compounds 2 and 4 exhibited low antimicrobial activity.

Molecular Cloning, Heterologous Expression, Purification, and Evaluation of Protein-Ligand Interactions of CYP51 of Candida krusei Azole-Resistant Fungal Strain

Due to the increasing prevalence of fungal diseases caused by fungi of the genus Candida and the development of pathogen resistance to available drugs, the need to find new effective antifungal agents has increased. Azole antifungals, which are inhibitors of sterol-14α-demethylase or CYP51, have been widely used in the treatment of fungal infections over the past two decades. Of special interest is the study of C. krusei CYP51, since this fungus exhibit resistance not only to azoles, but also to other antifungal drugs and there is no available information about the ligand-binding properties of CYP51 of this pathogen. We expressed recombinant C. krusei CYP51 in E. coli cells and obtained a highly purified protein. Application of the method of spectrophotometric titration allowed us to study the interaction of C. krusei CYP51 with various ligands. In the present work, the interaction of C. krusei CYP51 with azole inhibitors, and natural and synthesized steroid derivatives was evaluated. The obtained data indicate that the resistance of C. krusei to azoles is not due to the structural features of CYP51 of this microorganism, but rather to another mechanism. Promising ligands that demonstrated sufficiently strong binding in the micromolar range to C. krusei CYP51 were identified, including compounds 99 (Kd = 1.02 ± 0.14 µM) and Ch-4 (Kd = 6.95 ± 0.80 µM). The revealed structural features of the interaction of ligands with the active site of C. krusei CYP51 can be taken into account in the further development of new selective modulators of the activity of this enzyme.

Recombinant Analogs of Sea Anemone Kunitz-Type Peptides Influence P2X7 Receptor Activity in Neuro-2a Cells

Purinergic P2X7 receptors (P2X7) have now been proven to play an important role and represent an important therapeutic target in many pathological conditions including neurodegeneration. Here, we investigated the impact of peptides on purinergic signaling in Neuro-2a cells through the P2X7 subtype in in vitro models. We have found that a number of recombinant peptides, analogs of sea anemone Kunitz-type peptides, are able to influence the action of high concentrations of ATP and thereby reduce the toxic effects of ATP. The influx of calcium, as well as the fluorescent dye YO-PRO-1, was significantly suppressed by the studied peptides. Immunofluorescence experiments confirmed that the peptides reduce the P2X7 expression level in neuronal Neuro-2a cells. Two selected active peptides, HCRG1 and HCGS1.10, were found to specifically interact with the extracellular domain of P2X7 and formed stable complexes with the receptor in surface plasmon resonance experiments. The molecular docking approach allowed us to establish the putative binding sites of the most active HCRG1 peptide on the extracellular domain of the P2X7 homotrimer and propose a mechanism for regulating its function. Thus, our work demonstrates the ability of the Kunitz-type peptides to prevent neuronal death by affecting signaling through the P2X7 receptor.

Substrate-induced modulation of protein-protein interactions within human mitochondrial cytochrome P450-dependent system

Steroidogenesis is strictly regulated at multiple levels, as produced steroid hormones are crucial to maintain physiological functions. Cytochrome P450 enzymes are key players in adrenal steroid hormone biosynthesis and function within short redox-chains in mitochondria and endoplasmic reticulum. However, mechanisms regulating supply of reducing equivalents in the mitochondrial CYP-dependent system are not fully understood. In the present work, we aimed to estimate how the specific steroids, substrates, intermediates and products of multistep reactions modulate protein-protein interactions between adrenodoxin (Adx) and mitochondrial CYP11 s. Using the SPR technology we determined that steroid substrates affect affinity and stability of CYP11s-Adx complexes in an isoform-specific mode. In particular, cholesterol induces a 4-fold increase in the rate of CYP11A1 - Adx complex formation without significant effect on dissociation (koff decreased ∼1.5-fold), overall increasing complex affinity. At the same time steroid substrates decrease the affinity of both CYP11B1 - Adx and CYP11B2 - Adx complexes, predominantly reducing their stability (4-7 fold). This finding reveals differentiation of protein-protein interactions within the mitochondrial pool of CYPs, which have the same electron donor. The regulation of electron supply by the substrates might affect the overall steroid hormones production. Our experimental data provide further insight into protein-protein interactions within CYP-dependent redox chains involved in steroidogenesis.

[Screening of potential non-azole inhibitors of lanosterol14-alpha demethylase (CYP51) of Candida fungi]

Currently, opportunistic fungi of the genus Candida are the main causative agents of mycoses, which are especially severe upon condition of acquired immunodeficiency. The main target for the development of new antimycotics is the cytochrome P450 51 (CYP51) of the pathogenic fungus. Due to the widespread distribution of Candida strains resistancy to inhibitors of the azole class, the screening for CYP51 inhibitors both among non-azole compounds and among clinically used drugs repurposing as antimycotics is becoming urgent. To identify potential inhibitors from the non-azole group, an integrated approach was applied, including bioinformatics analysis, computer molecular modeling, and a surface plasmon resonance (SPR) technology. Using in silico modeling, the binding sites for acetylsalicylic acid, ibuprofen, chlorpromazine and haloperidol (this compounds, according to the literature, showed antimycotic activity) were predicted in the active site of CYP51 of Candida albicans and Candida glabrata. The Kd values of molecular complexes of acetylsalicylic acid, ibuprofen and haloperidol with CYP51, determined by SPR analysis, ranged from 18 μM to 126 μM. It was also shown that structural derivatives of haloperidol, containing various substituents, could be positioned in the active site of CYP51 of Candida albicans with the possible formation of coordination bonds between the hydroxyl groups of the derivatives and the iron atom in the heme of CYP51. Thus, the potential basic structures of non-azole compounds have been proposed, which can be used for the design of new CYP51 inhibitors of Candida fungi.

Mechanism of the Affinity-Enhancing Effect of Isatin on Human Ferrochelatase and Adrenodoxin Reductase Complex Formation: Implication for Protein Interactome Regulation

Isatin (indole-2, 3-dione) is a non-peptide endogenous bioregulator exhibiting a wide spectrum of biological activity, realized in the cell via interactions with numerous isatin-binding proteins, their complexes, and (sub) interactomes. There is increasing evidence that isatin may be involved in the regulation of complex formations by modulating the affinity of the interacting protein partners. Recently, using Surface Plasmon Resonance (SPR) analysis, we have found that isatin in a concentration dependent manner increased interaction between two human mitochondrial proteins, ferrochelatase (FECH), and adrenodoxine reductase (ADR). In this study, we have investigated the affinity-enhancing effect of isatin on the FECH/ADR interaction. The SPR analysis has shown that FECH forms not only homodimers, but also FECH/ADR heterodimers. The affinity-enhancing effect of isatin on the FECH/ADR interaction was highly specific and was not reproduced by structural analogues of isatin. Bioinformatic analysis performed using three dimensional (3D) models of the interacting proteins and in silico molecular docking revealed the most probable mechanism involving FECH/isatin/ADR ternary complex formation. In this complex, isatin is targeted to the interface of interacting FECH and ADR monomers, forming hydrogen bonds with both FECH and ADR. This is a new regulatory mechanism by which isatin can modulate protein-protein interactions (PPI).

[SPR analysis of protein-protein interactions with P450 cytochromes and cytochrome b5 integrated into lipid membrane]

Identification of new protein-protein interactions (PPI) and characterization of quantitative parameters of complex formation represent one of central tasks of protein interactomics. This work is a logical continuation of the cycle of our previous works devoted to the study of PPIs among the components of cytochrome P450-dependent monooxygenase system. Using an optical biosensor of Surface Plasmon Resonance (SPR biosensor), a comparative analysis on the determination of kinetic and equilibrium parameters of complex formation between the membrane-bound hemoprotein cytochrome b5 with cytochrome P450s was performed using two different protocols for protein immobilization: 1) covalent non-oriented one on to the carboxymethyl dextran chip type CM and 2) non-covalent oriented immobilization in the lipid environment on the chip type L1 with internal control of liposomes surface distribution. In the second protocol it was shown that the complex formation was characterized by 2.5 times higher affinity due to an decrease in rate dissociation constants. The appropriateness of using both experimental models is discussed.

New Targets of Kunitz-Type Peptide from Sea Anemone Heteractis magnifica

The interaction of Kunitz-type peptide, HMIQ3c1, from the sea anemone Heteractis magnifica with several serine proteases, including inflammatory proteases, was investigated using the surface plasmon resonance approach. We showed that the recombinant analog of HMIQ3c1 forms sufficiently strong complexes with trypsin (K_D = 1.07 × 10^-9 М) and chymotrypsin (K_D = 4.70 × 10^-8 М). Analysis of thermodynamic parameters of HMIQ3c1/chymotrypsin revealed significant contribution of the entropic factor to the complex formation. The formation of specific complexes of HMIQ3c1 with the kallikrein (K_D = 2.81 × 10^-8 М) and neutrophil elastase (K_D = 1.11 × 10^-7 М) indicates its anti-inflammatory activity and makes prospects to use the peptide as a potential therapeutic agent.

Insights into Ergosterol Peroxide's Trypanocidal Activity

Trypanosoma cruzi, which causes Chagas disease, is a significant health threat in many countries and affects millions of people. Given the magnitude of this disease, a broader understanding of trypanocidal mechanisms is needed to prevent and treat infection. Natural endoperoxides, such as ergosterol peroxide, have been shown to be toxic to parasites without causing harm to human cells or tissues. Although prior studies have demonstrated the trypanocidal activity of ergosterol peroxide, the cellular and molecular mechanisms remain unknown. The results of this study indicate that a free-radical reaction occurs in T. cruzi following ergosterol peroxide exposure, leading to cell death. Using a combination of biochemical, microscopic and in silico experimental approaches, we have identified, for the first time, the cellular and molecular cytotoxic mechanism of an ergosterol peroxide obtained from Pleurotus ostreatus (Jacq) P. Kumm. f. sp. Florida.

Affinity Isolation and Mass Spectrometry Identification of Prostacyclin Synthase (PTGIS) Subinteractome

Prostacyclin synthase (PTGIS; EC 5.3.99.4) catalyzes isomerization of prostaglandin H2 to prostacyclin, a potent vasodilator and inhibitor of platelet aggregation. At present, limited data exist on functional coupling and possible ways of regulating PTGIS due to insufficient information about protein-protein interactions in which this crucial enzyme is involved. The aim of this study is to isolate protein partners for PTGIS from rat tissue lysates. Using CNBr-activated Sepharose 4B with covalently immobilized PTGIS as an affinity sorbent, we confidently identified 58 unique proteins by mass spectrometry (LC-MS/MS). The participation of these proteins in lysate complex formation was characterized by SEC lysate profiling. Several potential members of the PTGIS subinteractome have been validated by surface plasmon resonance (SPR) analysis. SPR revealed that PTGIS interacted with full-length cytochrome P450 2J2 and glutathione S-transferase (GST). In addition, PTGIS was shown to bind synthetic peptides corresponding to sequences of for GSTA1, GSTM1, aldo-keto reductase (AKR1A1), glutaredoxin 3 (GLRX3) and histidine triad nucleotide binding protein 2 (HINT2). Prostacyclin synthase could potentially be involved in functional interactions with identified novel protein partners participating in iron and heme metabolism, oxidative stress, xenobiotic and drugs metabolism, glutathione and prostaglandin metabolism. The possible biological role of the recognized interaction is discussed in the context of PTGIS functioning.

[The analysis of participation of individual proteins in the protein interactome formation]

It becomes increasingly clear that most proteins of living systems exist as components of various protein complexes rather than individual molecules. The use of various proteomic techniques significantly extended our knowledge not only about functioning of individual complexes but also formed a basis for systemic analysis of protein-protein interactions. In this study gel-filtration chromatography accompanied by mass-spectrometry was used for the interactome analysis of human liver proteins. In six fractions (with average molecular masses of 45 kDa, 60 kDa, 85 kDa, 150 kDa, 250 kDa, and 440 kDa) 797 proteins were identified. In dependence of their distribution profiles in the fractions, these proteins could be subdivided into four groups: (1) single monomeric proteins that are not involved in formation of stable protein complexes; (2) proteins existing as homodimers or heterodimers with comparable partners; (3) proteins that are partially exist as monomers and partially as components of protein complexes; (4) proteins that do not exist in the monomolecular state, but also exist within protein complexes containing three or more subunits. Application of this approach to known isatin-binding proteins resulted in identification of proteins involved in formation of the homo- and heterodimers and mixed protein complexes.

Structural Analogues of Lanosterol from Marine Organisms of the Class Asteroidea as Potential Inhibitors of Human and Candida albicans Lanosterol 14α-demethylases

Lanosterol 14α-demethylases (hemoproteins of the cytochrome P450(51) family) are involved in biosynthesis of different membrane sterols, including animal cholesterol, fungal ergosterol and C24-modified plant and protozoa sterols. In this study we have investigated 10 structural analogs of lanosterol isolated from echinoderms belonging to the class Asteroidea as potential ligands (competitive inhibitors) of human and Candida albicans cytochromes P450(51). The study was performed using the surface plasmon resonance method, spectrophotometric titration and enzyme assay. Among the compounds tested we found several selective ligands for human and Candida albicans cytochromes. Between selective ligands of the human lanosterol 14α-demethylase we found two novel inhibitors of this enzyme: henricioside H1 and levisculoside G from Henricia derjugini. With due consideration of obtained data, we conclude that marine organisms from the class Asteroidea can be a valuable source of new lead compounds for creation of selective inhibitors of cytochromes P450(51) family with less side effects due to their selective action on these enzymes in different types of organisms.