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Identification, visualization, and quantitation of cardiolipin (CL) in biological membranes is of great interest because of the important structural and physiological roles of this lipid. Selective fluorescent detection of CL using noncovalently bound fluorophore 1,1,2,2-tetrakis[4-(2-trimethylammonioethoxy)-phenylethene (TTAPE-Me) has been recently proposed. However, this dye was only tested on wild-type mitochondria or liposomes containing negligible amounts of other anionic lipids, such as phosphatidylglycerol (PG) and phosphatidylserine (PS). No clear preference of TTAPE-Me for binding to CL compared to PG and PS was found in our experiments on artificial liposomes, Escherichia coli inside-out vesicles, or Saccharomyces cerevisiae mitochondria in vitro or in situ, respectively. The shapes of the emission spectra for these anionic phospholipids were also found to be indistinguishable. Thus, TTAPE-Me is not suitable for detection, visualization, and localization of CL in the presence of other anionic lipids present in substantial physiological amounts. Our experiments and complementary molecular dynamics simulations suggest that fluorescence intensity of TTAPE-Me is regulated by dynamic equilibrium between emitting dye aggregates, stabilized by unspecific but thermodynamically favorable electrostatic interactions with anionic lipids, and nonemitting dye monomers. These results should be taken into consideration when interpreting past and future results of CL detection and localization studies with this probe in vitro and in vivo. Provided methodology emphasizes minimal experimental requirements, which should be considered as a guideline during the development of novel lipid-specific probes.

Pristine graphene, a range of graphene oxides, and silica substrates were used to investigate the effect of surface hydrophilicity on supported lipid bilayers by means of all-atom molecular dynamics simulations. Supported 1,2-dioleoyl-sn-glycero-3-phosphocholine lipid bilayers were found in close-contact conformations with hydrophilic substrates with as low as 5% oxidation level, while self-assembled monolayers occur on pure hydrophobic graphene only. Lipids and water at the surface undergo large redistribution to maintain the stability of the supported bilayers. Deposition of bicelles on increasingly hydrophilic substrates shows the continuous process of reshaping of the supported system and makes intermediate stages between self-assembled monolayers and supported bilayers. The bilayer thickness changes with hydrophilicity in a complex manner, while the number of water molecules per lipid in the hydration layer increases together with hydrophilicity.

We demonstrate the construction of wavelength λ-ratiometric images that allow visualizing the distribution of microscopic dynamics within living cells and tissues by using the newly developed principle of fluorescence response. The bent-to-planar motion in the excited state of incorporated fluorescence probes leads to elongation of the π-delocalization, resulting in microviscosity-dependent but polarity-insensitive interplay between well-separated blue and red bands in emission spectra. This allows constructing the exceptionally contrasted images of cellular dynamics. Moreover, the application of probes with increased affinity toward biological membranes allowed detecting the differences in dynamics between the plasma membrane and intracellular membrane structures. Such λ-ratiometric microviscosity imaging was extended for mapping the living tissues and observing their inflammation-dependent changes.

Molecular modeling in pharmacology is a promising emerging tool for exploring drug interactions with cellular components. Recent advances in molecular simulations, big data analysis, and artificial intelligence (AI) have opened new opportunities for rationalizing drug interactions with their pharmacological targets. Despite the obvious utility and increasing impact of computational approaches, their development is not progressing at the same speed in different fields of pharmacology. Here, we review current in silico techniques used in cardiovascular diseases (CVDs), cardiological drug discovery, and assessment of cardiotoxicity. In silico techniques are paving the way to a new era in cardiovascular medicine, but their use somewhat lags behind that in other fields.

Solvent dependent photophysical properties of two chromone derivatives, namely 7-amino-2-methyl chromone (AMC) and 3-cyano chromone (CyC), were studied by time-resolved fluorescence spectroscopy, density functional theory (DFT) calculation and molecular dynamics (MD) simulation. Contributions from different solvatochromic parameters were quantitatively estimated using Lippert-Mataga relation, uni-parametric ET(30) and multi-parametric Kamlet–Taft and/or Catalan relations. Notable solvatochromic shift in emission peak was estimated for CyC (Δλ = 130 nm) in comparison with AMC (Δλ = 53 nm). While both solvent hydrogen bond donation acidity and acceptance basicity is important in AMC photophysics, the latter is insignificant for CyC. Estimation of hydrogen bonding pattern in hydrated structures of AMC and CyC derived from MD simulation reveals that specific hydrogen bond donation of the solvent to carbonyl oxygen of the chromones is the most important microstructure modulating the spectral behavior in both the cases, augmenting the experimental observation as well as DFT results.

The development of elongated nanoparticles for drug delivery is of growing interest in recent years, due to longer blood circulation and improved efficacy compared to spherical counterparts. Squalenoyl-doxorubicin (SQ-Dox) conjugate was previously shown to form elongated nanoparticles with improved therapeutic efficacy and decreased toxicity compared to free doxorubicin. By using experimental and computational techniques, we demonstrate here that the specific physical properties of SQ-Dox, which include stacking and electrostatic interactions of doxorubicin as well as hydrophobic interactions of squalene, are involved in the formation of nanoassemblies with diverse elongated structures. We show that SQ-Dox bioconjugate concentration, ionic strength, and anion nature can be used to modulate the shape and stiffness of SQ-Dox nanoparticles. As those parameters are involved in nanoparticle behavior in biological media, these findings could bring interesting opportunities for drug delivery and serve as an example for the design of original nanodrugs with stacking properties tuned for particular clinical purposes.

The mode of interaction of polyphenolic compounds like genistein (GTN) and ellagic acid (EGA) with human and bovine serum albumin (HSA and BSA, respectively) was found to differ significantly. Stern-Volmer (SV) analysis of the fluorescence quenching data revealed that the binding strength of EGA (1.9 ± 0.09 × 105 M−1) to HSA is about one order of magnitude higher than GTN (2.24 ± 0.06 × 104 M−1). While the static quenching of HSA fluorescence was found to proceed through simple Stern-Volmer (SV) mechanism, a quenching sphere-of-action model was indispensable for BSA. Temperature dependent fluorescence along with a series of other biophysical experiments and ensemble docking calculation revealed that EGA and GTN bind to the serum proteins primarily through the entropy driven process. The α-helical content and the microenvironment near Trp residue of HSA and BSA did not show any appreciable change due to the binding of either GTN or EGA. Interestingly, both GTN and EGA were found to inhibit the formation of advanced glycated end (AGE) product of serum proteins up to the extent of 70–90% within 12–24 h. Relatively moderate binding propensity along with the anti-glycation ability of the polyphenols confirmed that GTN and EGA can be used either as an alternative or towards development of suitable drugs in the prevention of many diabetic-related complications.

The EnCurv method for maintaining membrane curvature in molecular dynamics simulations is introduced. The method allows maintaining any desired curvature in a sector of lipid membrane bent in a single plane without adding any unphysical interactions into the system and without restrictions on lateral and transversal lipid diffusion and distribution. The current implementation is limited to the membranes curved in a single plane but generalization to arbitrary curvature and membrane topology is possible. The method is simple, easy to implement, and scales linearly with the system size. EnCurv is agnostic to the force field, simulation parameters, and membrane composition. The proof of principle implementation (https://github.com/yesint/EnCurv) is compatible with the majority of modern simulation packages and shows consistent results on the model systems.

free open access article 31 p.; International audience; In this work, we have explored natural unmodified low- and high-density lipoproteins (LDL and HDL) as selective delivery vectors in colorectal cancer therapy. We show in vitro in cultured cells and in vivo (NanoSPECT/CT) in the CT-26 mice colorectal cancer model that LDLs are mainly taken up by cancer cells, while HDLs are preferentially taken up by macrophages. We loaded LDLs with cisplatin and HDLs with the heat shock protein-70 inhibitor AC1LINNC, turning them into a pair of “Trojan horses” delivering drugs selectively to their target cells as demonstrated in vitro in human colorectal cancer cells and macrophages, and in vivo. Coupling of the drugs to lipoproteins and stability was assessed by mass and raman spectrometry analysis. Cisplatin vectorized in LDLs led to better tumor growth suppression with strongly reduced adverse effects such as a renal or liver toxicity. AC1LINNC vectorized into HDLs induced a strong oxidative burst in macrophages and innate anti-cancer immune response. Cumulative anti-tumor effect was observed for both drug-loaded lipoproteins. Altogether, our data show that lipoproteins from patient’s blood can be used as natural nanocarriers allowing cell specific targeting, paving the way toward more efficient, safer and personalized use of chemo-and immunotherapeutic drugs in cancer

Identification, visualization and quantitation of cardiolipin (CL) in biological membranes is of great interest due to important structural and physiological roles of this lipid. Selective fluorescent detection of CL using non-covalently bound fluorophore TTAPE-Me (1,1,2,2-tetrakis[4-(2-trimethylammonioethoxy)-phenylethene) has been recently proposed. However, this dye was only tested on wild-type mitochondria or liposomes containing neglegible amounts of other anionic lipids, such as PG and PS. No clear preference of TTAPE-Me for binding to CL compared to PG and PS was found in our experiments. The shapes of the emission spectra for these anionic phospholipids were also found to be indistinguishable. Our experiments and complementary molecular dynamics simulations suggest that fluorescence intensity of TTAPE-Me is regulated by dynamic equilibrium between emitting dye, bound to anionic lipids by means of unspecific electrostatic attraction, and non-emitting dye aggregates in aqueous solution. Therefore, TTAPE-Me is not suitable for detection, visualization and localization of CL in the presence of PS and PG present in physiological amounts in the membranes of eukaryotic and prokaryotic cells, respectively.

We demonstrate the construction of wavelength λ-ratiometric images that allow visualizing the distribution of microscopic dynamics within living cells and tissues by using the newly developed principle of fluorescence response. The bent-to-planar motion in the excited state of incorporated fluorescence probes leads to elongation of the π-delocalization, resulting in microviscosity-dependent but polarity-insensitive interplay between well-separated blue and red bands in emission spectra. This allows constructing the exceptionally contrasted images of cellular dynamics. Moreover, the application of probes with increased affinity toward biological membranes allowed detecting the differences in dynamics between the plasma membrane and intracellular membrane structures. Such λ-ratiometric microviscosity imaging was extended for mapping the living tissues and observing their inflammation-dependent changes.

The dynamics of solvation of an excited chromophore, 5-(4″-dimethylaminophenyl)-2-(4′-sulfophenyl)oxazole, sodium salt (DMO), has been explored in confined nanoscopic environments of β-cyclodextrin (βCD) and heptakis(2,6-di-O-methyl)-β-cyclodextrin (DIMEB). Solvation occurs on a distinctly slower time scale (τS3 ∼ 47 ps, τS4 ∼ 517 ps) in the host cavity of DIMEB than in that of βCD (τS3 ∼ 20 ps, τS4 ∼ 174 ps). The calculated equilibrium solvation response of DMO was characterized by four relaxation components (τS1 ∼ 0.46–0.48 ps, τS2 ∼ 3.2–3.4 ps, τS3 ∼ 32.3–37.7 ps, and τS4 ∼ 232–485 ps), of which the longer ones (τS3, τS4) are well-consistent with experiments, whereas the ultrafast components (τS1, τS2) are unresolved. The observed time constant (τS3) within the ∼20–47 ps range arises from slow water molecules in the primary hydration layers of the host CDs and is slower for DIMEB than for βCD presumably due to longer-lived and stronger hydrogen bonds that water forms with the former host relative to th...

In this research we investigate the connection between the cytoplasmic machinery of apoptosis and the plasma membrane organization by studying the coupling of caspase-3 activation and inhibition with PS exposure and the change of lipid order in plasma membrane sensed by a fluorescent membrane probe NR12S. First, we performed in silico molecular dynamics simulations, which suggest that the mechanism of response of NR12S to lipid order may combine both sensitivity to membrane polarity/hydration and change in the fluorophore orientation. Second, cellular studies revealed that upon triggering apoptosis with IPA-3 and camptothecin the NR12S response is similar to that observed after decrease of lipid order induced by cholesterol depletion, 7-ketocholesterol enrichment or sphingomyelin hydrolysis. NR12S response can be influenced by a caspase-3 inhibitor Z-DEVD-FMK. Flow cytometry data further indicate that the NR12S response correlates with the response of FITC-labeled DEVD-FMK peptide and GFP-labeled Annexin V on the whole time scale (0–24 h) of apoptosis induction by camptothecin. We conclude that fine changes in lipid order observed by NR12S are coupled with early steps of cellular events in apoptosis.

In this work the permeability of a model asymmetric plasma membrane, for ions, water and the anti-cancer drugs cisplatin and gemcitabine is studied by means of all-atom molecular dynamics simulations. It is shown that permeability of the membranes increases from one to three orders of magnitude upon membrane bending depending on the compound and the sign of curvature. Our results show that the membrane curvature is an important factor which should be considered during evaluation of drug translocation.TOC GRAPHICS

We demonstrate the construction of wavelength λ-ratiometric images that allow visualizing the distribution of microscopic dynamics within living cells and tissues by using the newly developed principle of fluorescence response. The bent-to-planar motion in the excited state of incorporated fluorescence probes leads to elongation of the π-delocalization, resulting in microviscosity-dependent but polarity-insensitive interplay between well-separated blue and red bands in emission spectra. This allows constructing the exceptionally contrasted images of cellular dynamics. Moreover, the application of probes with increased affinity towards biological membranes allowed detecting the differences in dynamics between plasma membrane and intracellular membrane structures. Such λ-ratiometric microviscosity imaging was extended for mapping the living tissues and observing their inflammation-dependent changes.

New technique of detecting lateral heterogeneity of the plasma membrane of living cells by means of membrane-binding fluorescent dyes is proposed. The kinetics of dye incorporation into the membrane or its lateral diffusion inside the membrane is measured and decomposed into exponential components by means of the Maximum Entropy Method. Two distinct exponential components are obtained consistently in all cases for several fluorescent dyes, two different cell lines and in different types of experiments including spectroscopy, flow cytometry and fluorescence recovery after photobleaching. These components are attributed to the liquid-ordered and disordered phases in the plasma membrane of studied cells in their dynamic equilibrium.

The effects of colloidal gold and silver nanoparticles (Au and Ag NP, respectively) were studied on the activity of acetylcholinesterase (AChE), the key enzyme in the pathology of Alzheimer's Disease (AD) and citrate synthase (CS), the mitochondrial enzyme responsible for oxidative metabolism. Being established as a primary basis of neurodegeneration, mitochondrial dysfunction connects both these two enzymes with AD. The in-vitro enzymatic activities are modulated strongly in presence of NPs. The maximum AChE catalytic rate (Vmax) increases by 30% in presence of NP systems. The Michalis-Menten constant (Km) remains unaltered in presence of AuNP; while, ~61.23% increase is noted in presence of AgNP. For the two-substrate enzyme CS, NPs were found to affect only the pathway involving oxaloacetate (OAA) as substrate. In this case, Vmax and Km increased by 21.80% and 46.60%, respectively for AuNP; while the corresponding increase were 18.20% and 33.33%, respectively for AgNP. The binding of AChE on AgNP surface occurred through random contact within very short time scale, followed by slower interaction and contact optimization within tens of nanoseconds. A series of cationic surfactants exhibited optimistic results in restoring the intrinsic activity for both the enzymes. The results highlight neurotoxicity of metal NPs in certain cases like AD and emphasize their use in pharmacological milieu only with suitable accompanying delivery medium like surfactants.

Comptes Rendus Chimie - In Press.Proof corrected by the author Available online since jeudi 22 mars 2018

In this work, realistic models of membranes of normal and cancer cells are developed. A special focus is given to their cholesterol content. It is shown that the loss of lipid asymmetry in the membranes of cancer cells leads to a decrease of their permeability to cisplatin by one order of magnitude in comparison to the membranes of normal cells. The change of cholesterol molar ratio from 0% to 33% also decreases the permeability of the membrane by approximately one order of magnitude. The permeability of pure DOPC membrane is 5-6 orders of magnitude higher than one of the membrane with realistic lipid composition, which makes it as an inadequate model for the studies of drug permeability.

The inhibitory efficacy of two substituted coumarin derivatives on the activity of neurodegenerative enzyme acetylcholinesterase (AChE) was assessed in aqueous buffer as well as in the presence of human serum albumin (HSA) and compared against standard cholinergic AD drug, Donepezil (DON). The experimental data revealed the inhibition to be of non-competitive type with both the systems showing substantial inhibitory activity on AChE. In fact, one of the tested compounds Chromenyl Coumarate (CC) was found to be better inhibitor (IC50 = 48.49 ± 5.6 nM) than the reference drug DON (IC50 = 74.13 ± 8.3 nM), unequivocally amplifying its importance. The structure of the compound was found to play a vital role in the inhibitory efficiency, validating previous Structure Activity Relationship (SAR) reviews for coumarin. The mechanism of inhibition remained impervious when the experimental medium was switched from aqueous buffer to HSA, albeit noticeable change in the inhibition potency of the compound 3, 3′- Methylene-bis (4-hydroxy coumarin) (MHC) (38%) and CC (35%). Both the coumarin derivatives were observed to bind to the peripheral anionic site (PAS) of AChE and also found to displace the fluorescence marker thioflavinT (ThT) from AChE binding pocket. All experimental observations were seconded by molecular docking and MD simulation results. The inferences drawn in this study form a foundation for further investigation on these compounds; magnifying the probability of their usage as AD drugs and re-emphasizes the significance of drug delivery media while considering the inhibition potencies of targeted drugs.

We have studied the interaction of three clinically promising squalenoylated drugs (gemcitabine-squalene, adenine-squalene, and doxorubicin-squalene) with low-density lipoproteins (LDL) by means of atomistic molecular dynamics simulations. It is shown that all studied squalenoylated drugs accumulate inside the LDL particles. This effect is promoted by the squalene moiety, which acts as an anchor and drives the hydrophilic drugs into the hydrophobic core of the LDL lipid droplet. Our data suggest that LDL particles could be a universal carriers of squalenoylated drugs in the bloodstream. Interaction of gemcitabine-squalene with human serum albumin (HSA) was also studied by ensemble of docking simulations. It is shown that HSA could also act as a passive carrier of this bioconjugate. It should be noted that the binding of squalene moiety to HSA was unspecific and did not occur in the binding pockets devoted to fatty acids.

Human tyrosyl-tRNA synthetase (HsTyrRS) is composed of two structural modules: N-terminal catalytic core and an EMAP II-like C-terminal domain. The structures of these modules are known, but no crystal structure of the full-length HsTyrRS is currently available. An all-atom model of the full-length HsTyrRS was developed in this work. The structure, dynamics, and domain binding interfaces of HsTyrRS were investigated by extensive molecular dynamics (MD) simulations. Our data suggest that HsTyrRS in solution consists of a number of compact asymmetric conformations, which differ significantly by their rigidity, internal mobility, orientation of C-terminal modules, and the strength of interdomain binding. Interfaces of domain binding obtained in MD simulations are in perfect agreement with our previous coarse-grained hierarchical rotations technique simulations. Formation of the hydrogen bonds between R93 residue of the ELR cytokine motif and the residues A340 and E479 in the C-module was observed. This observation supports the idea that the lack of cytokine activity in the full-length HsTyrRS is explained by interactions between N-modules and C-modules, which block the ELR motif. Copyright © 2013 John Wiley & Sons, Ltd.

Aim. In this work we developed a novel technique of obtaining the spectrum of conformational relaxations in a solvated protein using non-equilibrium molecular dynamics simulation. Methods. Structural relaxations in the protein are initiated by the abrupt jump of pressure in the NPT simulations. The change of the protein volume after the jump is monitored and the Maximum Entropy Method is used for spectral decomposition of the volume relaxation curve. The human serum albumin (HSA) is used as a test case. Results. The obtained relaxation spectrum of HSA contains one component attributed to the bulk water and five components caused by the relaxations of the protein globule and its hydration shell. All relaxation components are in good agreement with the available experimental data obtained by the time-resolved spectroscopy and the broadband acoustic spectroscopy of HSA. Conclusions. The developed technique allows obtaining spectra of conformational relaxations of soluble proteins in a range of time scales from ~0.1 ps to ~50 ns utilizing single non-equilibrium molecular dynamics simulation. Keywords: protein relaxations, molecular dynamics, maximum entropy method, pressure jump, HSA. Мета. Розробка методики, що дозволяє отримувати спектри конформаційних релаксацій сольватованого білка методом нерівноважної молекулярної динаміки. Методи. Структурну релаксацію білка ініціювали різкою зміною тиску у процесі розрахунку в NPT- ансамблі. Проведено спектральну декомпозицію кривої зміни об’єму білка після стрибка тиску методом максимальної ентропії. Результати. Одержаний спектр релаксацій містить один компонент, що належить до чистої води, і п’ять компонентів, віднесених до білка та його гідратної оболонки. Конформації всіх компонентів відповідають структурам, отриманим методами оптичної і акустичної спектроскопії. Висновки. Розроблена методика дозволяє розраховувати спектри структурної релаксації сольватованих білків у діапазоні часів від ~0,1 пс до ~50 нс з однієї траєк- торії, одержаної методом нерівноважної молекулярної динаміки. Ключові слова: релаксація білка, молекулярна динаміка, метод максимальної ентропії, стрибки тиску, сироватковий альбумін людини. Цель. Разработка новой методики получения спектра конформационных релаксаций сольватированного белка методом неравновесной молекулярной динамики. Методы. Структурную релаксацию белка инициировали резким изменением давления в процессе расчета в NPT-ансамбле. Проведена спектральная декомпозиция кривой изменения объема белка после скачка давления методом максимальной энтропии. В качестве тестового объекта использован сывороточный альбумин человека. Результаты. Полученный спектр релаксаций содержит один компонент, принадлежащий чистой воде, и пять компонентов, относящихся к белку и его гидратной оболочке. Конформации всех компонентов соответствуют таковым, полученным методами оптической и акустической спектроскопии. Выводы. Разработанная методика позволяет рассчитывать спектры конформационных релаксаций сольватированных белков в диапазоне времен от ~0,1 пс до ~50 нс из единственной траектории, вычисленной методом неравновесной молекулярной динамики. Ключевые слова: релаксация белка, молекулярная динамика, метод максимальной энтропии, скачки давления, сывороточный альбумин человека.

STAT3 protein, which is known to be involved in cancer development, is a promising target for anticancer therapy. Successful inhibitors of STAT3 should not affect an activity of closely related protein STAT1, which makes their development challenging. The mechanisms of selectivity of several existing STAT3 inhibitors are not clear. In this work, we studied molecular mechanisms of selectivity of 13 experimentally tested STAT3 inhibitors by means of extensive molecular dynamics and ensemble docking simulations. It is shown that all studied inhibitors bind to the large part of the protein surface in an unspecific statistical manner. The binding to the dimerization interface of the SH2 domain, which is usually considered as the main target region, is not energetically preferable. Binding in this region is remarkably similar for STAT1 and STAT3 proteins and cannot explain experimentally observed selectivity toward STAT3. We propose a new mechanism of selectivity called "selectivity by distraction" for existing STAT3 inhibitors. This mechanism is based on equilibrium statistical partitioning of inhibitor molecules between protein domains. The unspecific binding of inhibitors to the DNA-binding and the coil-coil domains is stronger in STAT1 in comparison to STAT3 while the energies of their binding to SH2 domains are comparable. This "distracts" inhibitor molecules from the SH2 domain of STAT1 and leads to higher effective concentration of inhibitors in the vicinity of the SH2 domain of STAT3.

Interaction of fullerenes with asymmetric and curved DOPC/DOPS bicelles is studied by means of coarse-grained molecular dynamics simulations. The effects caused by asymmetric lipid composition of the membrane leaflets and the curvature of the membrane are analyzed. It is shown that the aggregates of fullerenes prefer to penetrate into the membrane in the regions of the moderately positive mean curvature. Upon penetration into the hydrophobic core of the membrane fullerenes avoid the regions of the extreme positive or the negative curvature. Fullerenes increase the ordering of lipid tails, which are in direct contact with them, but do not influence other lipids significantly. Our data suggest that the effects of the membrane curvature should be taken into account in the studies concerning permeability of the membranes to fullerenes and fullerene-based drug delivery systems.

The distribution of cholesterol in asymmetric lipid bilayers was studied by extensive coarse-grained molecular dynamics simulations. The effects of the lipid head group charge, acyl chain saturation, spontaneous membrane curvature and surface tension of the membrane were investigated. Four asymmetric bilayers containing DOPC, DOPS, DSPC or DSPS lipids were simulated on a time scale extended to tens of microseconds. We show that cholesterol strongly prefers anionic lipids to neutral and saturated lipid tails to unsaturated with a distribution ratio of ~0.7 in neutral/anionic bilayers and of ~0.4 in unsaturated/saturated bilayers. Multiple flip-flop transitions of cholesterol were observed directly, and their mean times ranged from 80 to 250 ns. It was shown that the distribution of cholesterol in the asymmetric membrane depends not only on the type of lipid, but also on the local membrane curvature and the surface tension. The membrane curvature enhances the influence of the lipid head groups on cholesterol distribution, while non-optimal surface tension caused by different areas per lipid in different monolayers increases the effect of the lipid tail saturation. It was clearly seen that the monolayers of asymmetric bilayers are interdependent. Mean distances from the bilayer center to cholesterol molecules depend not only on the type of the lipid in the considered monolayer but also on the composition of the opposite monolayer.

Aminoacyl-tRNA synthetases are key enzymes of protein biosynthesis which usually possess multidomain structures. Mammalian tyrosyl-tRNA synthetase is composed of two structural modules: N-terminal catalytic core and an EMAPII-like C-terminal domain separated by long flexible linker. The structure of full-length human cytoplasmic tyrosyl-tRNA synthetase is still unknown. The structures of isolated N-terminal and C-terminal domains of the protein are resolved, but their compact packing in a functional enzyme is a subject of debates. In this work we studied putative compactization of the N- and C-terminal modules of human tyrosyl-tRNA synthetase by the coarse-grained hierarchical rotations technique (HIEROT). The large number of distinct types of binding interfaces between N- and C-terminal modules is revealed in the absence of enzyme substrates. The binding propensities of different residues are computed and several binding “hot spots” are observed on the surfaces of N and C modules. These results could be used to govern atomistic molecular dynamics simulations, which will sample preferable binding interfaces effectively.

The Hierarchical Domain-Wise Alignment (HDWA) technique of domain identification in proteins is presented. HDWA is designed to identify hierarchically organized dynamic domains in proteins using the MD trajectories by eliminating systematic motions from MD trajectories recursively in a model-free manner. The method is tested on the proteins from different structural classes.

The aim of this series of papers is to develop the semi-quantitative theory of the gating of KcsA channel. For this purpose the available structural and electrophysiological data and the results of molecular dynamics simulations were used in the context of the concept of dynamical self-organization. In the first paper we describe the simplified model of the geometry and energetics of the gating process. This work is the first successful attempt of combining the structure and dynamics of a real protein and the general concept of dynamic self-organization. Мета даної серії робіт полягає у розробці напівкількісної теорії воротних процесів в іонному каналі KcsA. Для цього залучено доступні експериментальні дані, а також результати молекулярної динаміки у контексті концепції динамічної самоорганізації. У першій роботі серії представлено спрощену модель геометрії та енергетики воротних процесів. Наведено першу успішну спробу об’єднання даних щодо структури та динаміки реального білка з концепцією динамічної самоорганізації. Целью данной серии работ является разработка полуколи- чественной теории воротных процессов в ионном канале KcsA. Для этого использованы доступные экспериментальные данные, а также результаты молекулярной динамики в контексте концепции динамической самоорганизации. В первой работе серии представлена упрощенная модель геометрии и энергетики воротных процессов. Приведена первая успешная попытка объединения данных о структуре и динамике реального белка с концепцией динамической самоорганизации.

Electrostatic fields generated on and inside biological membranes are recognized to play a fundamental role in key processes of cell functioning. Their understanding requires an adequate description on the level of elementary charges and the reconstruction of electrostatic potentials by integration over all elementary interactions. Out of all the available research tools, only molecular dynamics simulations are capable of this, extending from the atomic to the mesoscopic level of description on the required time and space scale. A complementary approach is that offered by molecular probe methods, with the application of electrochromic dyes. Highly sensitive to intermolecular interactions, they generate integrated signals arising from electric fields produced by elementary charges at the sites of their location. This review is an attempt to provide a critical analysis of these two approaches and their present and potential applications. The results obtained by both methods are consistent in that they both show an extremely complex profile of the electric field in the membrane. The nanoscopic view, with two-dimensional averaging over the bilayer plane and formal separation of the electrostatic potential into surface (Psi(s)), dipole (Psi(d)) and transmembrane (Psi(t)) potentials, is constructive in the analysis of different functional properties of membranes.

The hinge-bending proteins provide the most pronounced example of the large-amplitude slow motions in a number of proteins, which are critical for their functioning. They are often used as the test ground for developing novel approaches to the simulation of slow protein dynamics. In the present study, we present the algorithm, which allows physically-consistent simulations of slow protein dynamics in globular proteins. Our algorithm is based on the hierarchical clustering of the correlation patterns (HCCP) technique of domain identification, which allows subdividing the protein into the hierarchy of the rigid-body-like clusters. The clusters are allowed to rotate relative to one another on the automatically identified hinges. The clusters are found in the course of automated, objective and well-tested procedure. In the present communication, our technique is applied to 10 hinge-bending proteins. For each of the proteins, we performed the blind search for the closed conformation, staring from the open one. Resulting closed conformations are compared with the closed states observed in crystallographic structures. It is shown that our technique produces realistic closed conformations for 8 out of 10 studied proteins. This demonstrates that HCCP technique can be used for finding alternative protein conformations and for sampling the slow motions in proteins.

International audience; Parameterization of molecular complexes containing a metallic compound, such as cisplatin, is challenging due to the unconventional coordination nature of the bonds which involve platinum atoms. In this work, we develop a new methodology of parameterization for such compounds based onquantum dynamics (QD) calculations. We show that the coordination bonds and angles are more flexible than in normal covalent compounds. The influence of explicit solvent is also shown to be crucial to determine the flexibility of cisplatin in quantum dynamics simulations. Two empirical topologies of cisplatin were produced by fitting its atomic fluctuations against QD in vacuum and QD with explicit first solvation shell of water molecules respectively. A third topology built in a standard way from the static optimized structure was used for comparison. The later one leads to an excessively rigid molecule and exhibits much smaller fluctuations of the bonds and angles than QD reveals. It is shown that accounting for thehigh flexibility of cisplatin molecule is needed for adequate description of its first hydration shell. MD simulations with flexible QD-based topology also reveal a significant decrease of the barrier of passive diffusion of cisplatin accross the model lipid bilayer. These results confirm that flexibility of organ-ometallic compounds is an important feature to be considered in classical molecular dynamics topologies. Proposed methodology based on QD simulations provides a systematic way of building such topologies.

The development of inhibitors blocking STAT3 transcriptional activity is a promising therapeutic approach against cancer and inflammatory diseases. In this context, the selectivity of inhibitors against the STAT1 transcription factor is crucial as STAT3 and STAT1 play opposite roles in the apoptosis of tumor cells and polarization of the immune response. A structure-based virtual screening followed by a luciferase-containing promoter assay on STAT3 and STAT1 signaling were used to identify a selective STAT3 inhibitor. An important role of the aminotetrazole group in modulating STAT3 and STAT1 inhibitory activities has been established. Optimization of the hit compound leads to 23. This compound inhibits growth and survival of cells with STAT3 signaling pathway while displaying a minimal effect on STAT1 signaling. Moreover, it prevents lymphocyte T polarization into Th17 and Treg without affecting their differentiation into Th1 lymphocyte.

NMR diffusometry has been gaining wide popularity in various areas of applied chemistry for investigating diffusion and complexation processes in solid and aqueous phases. To date, the application of this method to study aggregation phenomena proceeding beyond the dimer stage of assembly has been restricted by the need for a priori knowledge of the aggregates’ shape, commonly difficult to know in practice. We describe here a comprehensive analysis of aggregation parameter-dependency on the type and shape selected for modeling assembly processes, and report for the first time a shape-independent model (designated the SHIM approach), which may be used as an alternative in cases when information on aggregates’ shapes is unavailable. The model can be used for determining equilibrium aggregation parameters from self-diffusion NMR data including equilibrium self-association constant and changes in enthalpy, ΔH, and entropy, ΔS.

A mechanism of barrier-less knock-on conduction is postulated for the best-studied KcsA ion channel. The conduction proceeds as follows: an ion enters the channel, which already contains two ions and “push” them along the pore. As a result, the state of triple occupancy forms. Eventually, the ion from the opposite side escapes to solution and the state of double occupancy is restored. The energies of the states with double and triple occupancies are almost the same, which makes alternation of these states possible. However, it is not known whether this mechanism is universal or specific for a narrow class of KcsA-like channels, which can accommodate just two or three ions in the selectivity filter. In the present work we develop a simplified model of the ion channel selectivity filter, which allows us to study the conduction in a broad range of ion occupancies using the Brownian dynamics. We show that knock-on barrier-less conduction occurs when the energies of adjacent equilibrium occupancy states are the same, regardless of the exact number of ions accommodated in the channel. It is shown that the maximal possible current flows through the channel in the regime of knock-on conduction. This allows us to conclude that knock-on barrier-less conduction can be considered as a universal mechanism of ions’ translocation in the ion channels with multiple occupancy.

Asymmetric lipid composition of the cell membranes plays an important role in the multitude of important biological functions. Much less is known, however, about the distribution and dynamics of cholesterol in asymmetric biological membranes. In this work we show how this issue could be addressed computationally by molecular dynamics simulations. The influence of the lipid head group charge, acyl chain saturation, spontaneous membrane curvature and the surface tension of the membrane on cholesterol distribution in asymmetric lipid bilayers is investigated. Four asymmetric bilayers containing DOPC, DOPS, DSPC, or DSPS lipids, were simulated on the time scale extended to tens of microseconds. We show that cholesterol strongly prefers anionic lipids to neutral and saturated lipid tails to unsaturated with distribution ratio ~0.4-0.6. Multiple flip-flop transitions of cholesterol were observed directly and their mean times range from 350 to 2,000 ns. It was shown that the distribution of cholesterol in the asymmetric bilayer depends not only on the type of lipids but also on the local membrane curvature and the surface tension. The geometric shape of spontaneously curved asymmetric bilayer changes dramatically in the presence of cholesterol. The membrane curvature becomes less homogeneous with large patches of flattened regions interleaved by rather sharp bends.

Asymmetric lipid composition of the cell membranes plays an important role in the multitude of important biological functions. Much less is known, however, about the distribution and dynamics of cholesterol in asymmetric biological membranes. In this work we show how this issue could be addressed computationally by molecular dynamics simulations. The influence of the lipid head group charge, acyl chain saturation, spontaneous membrane curvature and the surface tension of the membrane on cholesterol distribution in asymmetric lipid bilayers is investigated. Four asymmetric bilayers containing DOPC, DOPS, DSPC, or DSPS lipids, were simulated on the time scale extended to tens of microseconds. We show that cholesterol strongly prefers anionic lipids to neutral and saturated lipid tails to unsaturated with distribution ratio ~0.4-0.6. Multiple flip-flop transitions of cholesterol were observed directly and their mean times range from 350 to 2,000 ns. It was shown that the distribution of cholesterol in the asymmetric bilayer depends not only on the type of lipids but also on the local membrane curvature and the surface tension. The geometric shape of spontaneously curved asymmetric bilayer changes dramatically in the presence of cholesterol. The membrane curvature becomes less homogeneous with large patches of flattened regions interleaved by rather sharp bends.

International audience; The curvature of biological membranes is known to be an important influence on important phenomena such as membrane fusion, endocytosis, and the functioning of integral membrane proteins. There is a growing demand for analytical tools that are able accommodate molecular dynamics trajectories of significantly curved lipid bilayers. In this work, an algorithm for determining the shape and curvature of a nonplanar lipid bilayer in molecular dynamics simulations is proposed. The algorithm calculates the coordinates of the midline and the curvature of the bilayer as well as the local normal to it at any point on the membrane, which is bent arbitrarily in a single plane and is topologically equivalent to an infinite bilayer. The algorithm is implemented as a C++ program and tested by exploring the molecular dynamic trajectories of a highly curved meander-like asymmetric lipid bilayer. The algorithm is general enough to allow it to be easily applied to other geometries of nonplanar membrane systems.

Although molecular dynamics simulations of highly curved lipid bilayers have become increasingly popular in recent years, there is no simple and general method of computing the shape and curvature of the bilayer, which is bent arbitrarily in three dimensions. In this work we propose a method, which allows computing local normal, mean and Gaussian curvatures at any point of an arbitrarily curved lipid membrane using molecular dynamics trajectories. The method is based on the analysis of local membrane patches and is applicable to the membranes of any shape and topology – bilayers, vesicles, micelles, bicelles, etc. The method is applied to a highly curved asymmetric DOPC/DOPS lipid bilayer simulated by means of extended coarse-grained molecular dynamics simulations. It is shown that addition of cholesterol makes the membrane more topologically heterogeneous by increasing the content of highly curved regions with either saddle-like or sphere-like topology. The topology of the DOPS lipid domains is more sensitive to the addition of cholesterol than DOPC domains.

The photophysics of 2-(2′-benzofuryl)-3-hydroxychromone (BFHC) is remarkably modulated in its complexes with macrocyclic hosts such as β-cyclodextrin (β-CD), hydroxypropyl-β-cyclodextrin (HP-β-CD) and methyl-β-cyclodextrin (M-β-CD). BFHC exhibits dual emission bands, attributable to excited normal (N*) and tautomer (T*) forms, where the latter originates from the former through an excited-state intramolecular proton transfer (ESIPT) reaction. Fluorescence lifetimes of the tautomer, along with the intensity ratio (IT*/IN*) of the dual emission bands, and the fluorescence quantum yield (Φ) of the dye, increase significantly in the order β-CD < HP-β-CD < M-β-CD to indicate increasing hydrophobicity of the dye environment in the host CD cavity. In accordance with this increasing hydrophobicity of the dye environment, the ESIPT dynamics of BFHC becomes increasingly fast in the host cavity in the order β-CD < HP-β-CD < M-β-CD. Binding constant data and molecular modeling studies indicate that the increasing order of the faster ESIPT dynamics originates from an increasingly tight host–guest spatial fit, which causes increasingly strong dehydration of the BFHC dye. Steric compatibility in size and shape between the host cavity and the guest, which modulates the tightness of the host–guest spatial fit and hence the extent of hydration, is a key factor for tuning the proton transfer dynamics since water molecules perturb the ESIPT reaction and quench the fluorescence of BFHC.