Molecular interaction of human serum albumin with paracetamol: Spectroscopic and molecular modeling studies

The interaction between paracetamol and human serum albumin (HSA) under physiological conditions has been investigated by fluorescence, circular dichroism (CD) and docking. Fluorescence data revealed that the fluorescence quenching of HSA by paracetamol was the result of the formed complex of HSA–paracetamol, and the binding constant (K_a) and binding number obtained is 1.3 × 10⁴ at 298 K and 2, respectively for the primary binding site. Circular dichorism spectra showed the induced conformational changes in HSA by the binding of paracetamol. Moreover, protein–ligand docking study indicated that paracetamols (two paracetamols bind to HSA) bind to residues located in the subdomain IIIA.     

Study of the interaction of human serum albumin with Alstonia scholaris leaf extract-mediated silver nanoparticles having bactericidal property

This study investigates the green synthesis of AgNPs from 1 mM aqueous AgNO₃ using 10% leaf extract of Alstonia scholaris (Chhatim) for its wide antibacterial and medicinal properties. The synthesized AgNPs were duly characterized by UV–vis (UV–vis) spectrophotometry, dynamic light scattering, field emission scanning electron microscopy, transmission electron microscopy, energy-dispersive analysis of X-rays spectroscopy, and fourier transform infrared spectrophotometry. Their antibacterial property was tested against Escherichia coli (ATCC 25922), and minimum inhibitory concentrations of 0.08 nM of AgNPs were obtained, which suggests improved therapeutic efficacy. We report the interaction of human serum albumin (HSA) with this nanoparticle, and this interaction was studied by UV–vis, fluorescence, and circular dichroism spectroscopies and zeta potential measurement at room temperature. It was found that the AgNPs form a complex with HSA, which may cause the slightest change in the conformation of HSA. The calculated values of Stern-Volmer quenching constant, binding constant, and binding distance were 1.82 × 10⁷ M⁻¹, 1.58 × 10⁷ M⁻¹, and 3.68 nm, respectively. Therefore, in future, the present study may provide useful information to design a better antibacterial compound by using green synthesized nanoparticles with fewer side effects.     

Kinetics parameter estimation for the binding process of salicylic acid to human serum albumin (HSA) with capacitive sensing technique

A novel method for real-time investigating the binding interaction between human serum albumin (HSA) and salicylic acid with capacitive sensing technique was successfully proposed. HSA was immobilized on the surface of a gold electrode modified with an insulating poly (o-phenylenediamine) (o-PD) film and colloid Au nanoparticles layers. The bioactivity of HSA was remained and major binding sites were available because of the excellent biocompatibility of gold nanoparticles. The capacitance and interfacial electron resistance of the sensor were altered, owing to the binding of HSA to salicylic acid. The time courses of the capacitance change were acquired with capacitive sensing technique during the binding process. Based on the capacitance response curves with time, the response model for the binding was derived in theory and the corresponding regression parameters were determined by fitting the real-time experimental data to the model. The binding and the dissociation rate constants (k₁ and k_− 1) were estimated to be 54.8 (mol l^− 1)^− 1 s^− 1 and 2.9 × 10^− 3 s^− 1, respectively. And the binding equilibrium constant (K_a) was calculated to be 1.89 × 10⁴ (mol l^− 1)^− 1.     

Interaction of prodigiosin with HSA and β-Lg: Spectroscopic and molecular docking studies

Human serum albumin (HSA) and bovine β-lactoglobulin (β-Lg) are both introduced as blood and oral carrier scaffolds with high affinity for a wide range of pharmaceutical compounds. Prodigiosin, a natural three pyrrolic compound produced by Serratia marcescens, exhibits many pharmaceutical properties associated with health benefits. In the present study, the interaction of prodigiosin with HSA and β-Lg was investigated using fluorescence spectroscopy, circular dichroism (CD) and computational docking. Prodigiosin interacts with the Sudlow’s site I of HSA and the calyx of β-Lg with association constant of 4.41 × 10⁴ and 1.99 × 10⁴ M⁻¹ to form 1:1 and 2:3 complexes at 300 K, respectively. The results indicated that binding of prodigiosin to HSA and β-Lg caused strong fluorescence quenching of both proteins through static quenching mechanism. Electrostatic and hydrophobic interactions are the major forces in the stability of PG–HSA complex with enthalpy- and entropy-driving mode, although the formation of prodigiosin–β-Lg complex is entropy-driven hydrophobic associations. CD spectra showed slight conformational changes in both proteins due to the binding of prodigiosin. Moreover, the ligand displacement assay, pH-dependent interaction and protein–ligand docking study confirmed that the prodigiosin binds to residues located in the subdomain IIA and IIIA of HSA and central calyx of β-Lg.     

An insight to the binding of ellagic acid with human serum albumin using spectroscopic and isothermal calorimetry studies

Ellagic acid (EA), a natural polyphenol evidence several pharmacological benefits. The binding profile of EA with human serum albumin (HSA) has been explored and investigated by Isothermal titration calorimetry (ITC), circular dichroism (CD) spectroscopy, time-correlated single-photon counting (TCSPC), absorbance spectroscopy, steady-state fluorescence spectroscopy, and modelling studies. The ITC data analysis revealed the binding Constant (K_a), ΔH, ΔS and ΔG values to be 15.5×10⁴M^?1, ?116.2±18.1 Kcal mol^?1, ?366 cal mol^?1K^?1 and ?7.13 Kcal mol^?1 respectively with a unique binding site at HSA. EA effectively quenched the intrinsic fluorescence of HSA by static quenching, whereas TCSPC data also revealed association of dynamic quenching also. Thermodynamic analysis confirmed that hydrophobic and mainly hydrogen bonding interaction played important role in stabilizing the HSA-EA complex. It further dictates the binding reaction to be enthalpy driven. The secondary structure of HSA was altered upon binding with EA. CD spectroscopic data indicated the fraction of alpha helicity to be decreased from 52% to 40% upon binding to EA. This study will provide an insight on evaluation of this bioactive interaction during transport and releasing efficiency at the target site in human physiological system since HSA is the most important carrier protein in blood serum.     

Investigating the binding interactions of galantamine with β-amyloid peptide

The anti-Alzheimer’s agent galantamine is known to possess anti-amyloid properties. However the exact mechanisms are not clear. We studied the binding interactions of galantamine with amyloid peptide dimer (Aβ_1–40) through molecular docking and molecular dynamics simulations. Galantamine’s binding site within the amyloid peptide dimer was identified by docking experiments and the most stable complex was analyzed by molecular dynamics simulation. These studies show that galantamine was interacting with the central region of the amyloid dimer (Lys16–Ala21) and the C-terminal region (Ile31–Val36) with minimum structural drift of Cα atom in those regions. Strikingly, a significant drift was observed at the turn region from Asp23-Gly29 (Cα atom RMSD = 9.2 Å and 11.6 Å at 50 fs and 100 fs respectively). Furthermore, galantamine’s binding mode disrupts the key pi–pi stacking interaction between aromatic rings of Phe19 (chain A) and Phe19 (chain B) and intermolecular hydrogen bonds seen in unbound peptide dimer. Noticeably, the azepine tertiary nitrogen of galantamine was in close proximity to backbone CO of Leu34 (distance <3.5 Å) to stabilize the dimer conformation. In summary, the results indicate that galantamine binding to amyloid peptide dimer leads to a significant conformational change at the turn region (Asp23–Gly29) that disrupts interactions between individual β-strands and promotes a nontoxic conformation of Aβ_1–40 to prevent the formation of neurotoxic oligomers.     

Comparative structural studies of two natural isoforms of ammodytoxin,phospholipases A2 from Vipera ammodytes ammodytes which differ in neurotoxicity and anticoagulant activity

Ammodytoxin A (AtxA) and its natural isoform AtxC from the venom of Vipera ammodytes ammodytes belong to group IIA-secreted phospholipases A₂ which catalyze the hydrolysis of glycerophospholipids and exhibit strong neurotoxic and anticoagulant effects. The two isoforms, which differ in sequence by only two amino acid residues (Phe124 > Ile and Lys128 > Glu), display significant differences in toxicity and anticoagulant properties and act on protein targets including neurotoxic proteic receptors and coagulation factor Xa with significantly different strengths of binding.In order to characterize the structural basis of these functional differences, we have determined the crystal structures of the two isoforms. Comparison of the structures shows that the mutation Lys128 > Glu in AtxC could perturb interactions with FXa, resulting in lower anticoagulant activity, since the side chain of Glu128 is partly buried, making a stabilizing hydrogen bond with the main-chain nitrogen atom of residue Thr35. This interaction leads to a displacement of the main polypeptide chain at positions 127 and 128 (identified by mutagenesis as important for interaction with FXa), and a different orientation of the side chain of unmutated Lys127. The mutation Phe124 > Ile in AtxC induces no significant conformational changes, suggesting that the differences in toxicity of the two isoforms are due essentially to differences in surface complementarity in the interaction of the toxin with the neurotoxic protein receptor. The crystal structures also reveal a novel dimeric quaternary association involving significant hydrophobic interactions between the N-terminal α-helices of two molecules of ammodytoxin related by crystallographic symmetry. Interactions at the dimer interface include important contributions from Met7, which is unique to ammodytoxin. Equilibrium sedimentation experiments are consistent with the crystallographic model.Competition experiments using SPR technology show complete inhibition of AtxA binding to FXa by calmodulin (CaM). The crystal structure shows that the C-terminal region, important for binding to FXa and CaM, is fully exposed and accessible for interaction with proteic receptors in both the monomeric and dimeric forms of ammodytoxin described here.     

Association between polymorphisms of matrix metalloproteinase 11 (MMP-11) and Kawasaki disease in the Korean population

AimsThis study was conducted to investigate the associations between single nucleotide polymorphisms (SNPs) of matrix metalloproteinases (MMPs) and Kawasaki disease (KD) in the Korean population.Main methodsA total 0f 101 KD patients and 306 healthy controls were examined. MMP7 (rs10502001, G/A, Arg77His), MMP11 (rs738792, T/C, Ala38Val), MMP12 (rs652438, A/G, Ile357Val) and MMP26 (rs2499953, A/G, Lys43Glu) genes were genotyped from the genomic DNA using direct sequencing. The results were then analyzed using logistic regression models, adjusting for gender as covariates.Key findingsThe four SNPs were in Hardy–Weinberg equilibrium. Only the MMP11 polymorphism (rs738792) was associated with KD. The SNP (rs738792) showed a statistically significant association with KD in the codominant (OR = 1.61, 95% CI = 1.11–2.34, P = 0.011) and dominant (OR = 1.92, 95% CI = 1.21–3.06, P = 0.006) models. However, there was no association between polymorphisms of other MMP genes and KD.SignificanceOverall, the results of this study indicate that MMP11 polymorphism may be associated with KD in the Korean population.     

First proof of bismuth oxide nanoparticles as efficient radiosensitisers on highly radioresistant cancer cells

This study provides the first proof of the novel application of bismuth oxide as a radiosensitiser. It was shown that on the highly radioresistant 9L gliosarcoma cell line, bismuth oxide nanoparticles sensitise to both kilovoltage (kVp) or megavoltage (MV) X-rays radiation. 9L cells were exposed to a concentration of 50 μg.mL⁻¹ of nanoparticle before irradiation at 125 kVp and 10 MV. Sensitisation enhancement ratios of 1.48 and 1.25 for 125 kVp and 10 MV were obtained in vitro, respectively. The radiation enhancement of the nanoparticles is postulated to be a combination of the high Z nature of the bismuth (Z = 83), and the surface chemistry. Monte Carlo simulations were performed to elucidate the physical interactions between the incident radiation and the nanoparticle. The results of this work show that Bi₂O₃ nanoparticles increase the radiosensitivity of 9L gliosarcoma tumour cells for both kVp and MV energies. Monte Carlo simulations demonstrate the advantage of a platelet morphology.     

Protective role against hydrogen peroxide and fibroblast stimulation via Ce-doped TiO2 nanostructured materials

BackgroundCerium oxide (CeO₂) and Ce-doped nanostructured materials (NMs) are being seen as innovative therapeutic tools due to their exceptional antioxidant effects; nevertheless their bio-applications are still in their infancy.MethodsTiO₂, Ce–TiO₂ and CeO₂–TiO₂ NMs were synthesized by a bottom-up microemulsion-mediated strategy and calcined during 7 h at 650 °C under air flux. The samples were compared to elucidate the physicochemical characteristics that determine cellular uptake, toxicity and the influence of redox balance between the Ce^3 +/Ce^4 + on the cytoprotective role against an exogenous ROS source: H₂O₂. Fibroblasts were selected as a cell model because of their participation in wound healing and fibrotic diseases.ResultsCe–TiO₂ NM obtained via sol–gel reaction chemistry of metallic organic precursors exerts a real cytoprotective effect against H₂O₂ over fibroblast proliferation, while CeO₂ pre-formed nanoparticles incorporated to TiO₂ crystalline matrix lead to a harmful CeO₂–TiO₂ material. TiO₂ was processed by the same pathways as Ce–TiO₂ and CeO₂–TiO₂ NM but did not elicit any adverse or protective influence compared to controls.ConclusionsIt was found that the Ce atoms source and its concentration have a clear effect on material's physicochemical properties and its subsequent influence in the cellular response. It can induce a range of biological reactions that vary from cytotoxic to cytoprotective.General significanceEven though there are still some unresolved issues and challenges, the unique physical and chemical properties of Ce-based NMs are fascinating and versatile resources for different biomedical applications.     

Comparative serum albumin interactions and antitumor effects of Au(III) and Ga(III) ions

In the present study, interactions of Au(III) and Ga(III) ions on human serum albumin (HSA) were studied comparatively via spectroscopic and thermal analysis methods: UV–vis absorbance spectroscopy, fluorescence spectroscopy, Fourier transform infrared (FT-IR) spectroscopy and isothermal titration calorimetry (ITC). The potential antitumor effects of these ions were studied on MCF-7 cells via Alamar blue assay. It was found that both Au(III) and Ga(III) ions can interact with HSA, however; Au(III) ions interact with HSA more favorably and with a higher affinity. FT-IR second derivative analysis results demonstrated that, high concentrations of both metal ions led to a considerable decrease in the α-helix content of HSA; while Au(III) led to around 5% of decrease in the α-helix content at 200 μM, it was around 1% for Ga(III) at the same concentration. Calorimetric analysis gave the binding kinetics of metal–HSA interactions; while the binding affinity (K_a) of Au(III)–HSA binding was around 3.87 × 10⁵ M⁻¹, it was around 9.68 × 10³ M⁻¹ for Ga(III)–HSA binding. Spectroscopy studies overall suggest that both metal ions have significant effects on the chemical structure of HSA, including the secondary structure alterations. Antitumor activity studies on MCF7 tumor cell line with both metal ions revealed that, Au(III) ions have a higher antiproliferative activity compared to Ga(III) ions.     

Analysis of lidocaine interactions with serum proteins using high-performance affinity chromatography

High-performance affinity chromatography was used to study binding by the drug lidocaine to human serum albumin (HSA) and α₁-acid glycoprotein (AGP). AGP had strong binding to lidocaine, with an association equilibrium constant (K_a) of 1.1–1.7 × 10⁵ M^?1 at 37 °C and pH 7.4. Lidocaine had weak to moderate binding to HSA, with a K_a in the range of 10³ to 10⁴ M^?1. Competitive experiments with site selective probes showed that lidocaine was interacting with Sudlow site II of HSA and the propranolol site of AGP. These results agree with previous observations in the literature and provide a better quantitative understanding of how lidocaine binds to these serum proteins and is transported in the circulation. This study also demonstrates how HPAC can be used to examine the binding of a drug with multiple serum proteins and provide detailed information on the interaction sites and equilibrium constants that are involved in such processes.     

A new type of neuron-specific aminopeptidase NAP-2 in rat brain synaptosomes

A novel neutral aminopeptidase (NAP-2) was found exclusively in the rat central nervous system (CNS). It was separated from the ubiquitous puromycin-sensitive aminopeptidase (PSA) and the neuron-specific aminopeptidase (NAP) by an automated FPLC-aminopeptidase analyzer. The activity of the neuronal aminopeptidase enriched in the synaptosomes is different from NAP and PSA in distribution and during brain development. The enzyme was purified 2230-fold to apparent homogeneity from rat brain cytosol with 4% recovery by ammonium sulfate fractionation, followed by column chromatography successively on Phenyl-Sepharose, Q-Sepharose, Sephadex G-200, and Mono Q. The single-chain enzyme with a molecular mass of 110 kDa has an optimal pH of 7.0 and a pI of 5.6. It splits β-naphthylamides of amino acid with aliphatic, polar uncharged, positively charged, and aromatic side chain. Leucyl β-naphthylamide (Leu βNA) is the best substrate with the highest hydrolytic coefficiency followed by Met βNA = Arg βNA = Lys βNA > Ala βNA > Tyr βNA > Phe βNA. The cysteine-, metallo-, glyco-aminopeptidase releases the N-terminal Tyr from Leu-enkephalin with a K_m 82 μM and a k_cat of 1.08 s⁻¹, and Met-enkephalin with a K_m of 106 μM and a k_cat of 2.6 s⁻¹. The puromycin-sensitive enzyme is most susceptible to amastatin with an IC₅₀ of 0.05 μM. The data indicate that the enzyme is a new type of NAP found in rodent. Its possible function in neuron growth, neurodegeneration, and carcinomas is discussed.     

Importance of conserved N-domain residues Thr441, Glu442, Lys515, Arg560, and Leu562 of sarcoplasmic reticulum Ca2+-ATPase for MgATP binding and subsequent catalytic steps. Plasticity of the nucleotide-binding site

Nine single mutations were introduced to amino acid residues Thr441, Glu442, Lys515, Arg560, Cys561, and Leu562 located in the nucleotide-binding domain of sarcoplasmic reticulum Ca2+-ATPase, and the functional consequences were studied in a direct nucleotide binding assay, as well as by steady-state and transient kinetic measurements of the overall and partial reactions of the transport cycle. Some partial reaction steps were also examined in mutants with alterations to Phe487, Arg489, and Lys492. The results implicate all these residues, except Cys561, in high affinity nucleotide binding at the substrate site. Mutations Thr441 --> Ala, Glu442 --> Ala, and Leu562 --> Phe were more detrimental to MgATP binding than to ATP binding, thus pointing to a role for these residues in the binding of Mg2+ or to a difference between the interactions with MgATP and ATP. Subsequent catalytic steps were also selectively affected by the mutations, showing the involvement of the nucleotide-binding domain in these reactions. Mutation of Arg560 inhibited phosphoryl transfer but enhanced the E1PCa2 --> E2P conformational transition, whereas mutations Thr441 --> Ala, Glu442 --> Ala, Lys492 --> Leu, and Lys515 --> Ala inhibited the E1PCa2 --> E2P transition. Hydrolysis of the E2P phosphoenzyme intermediate was enhanced in Glu442 --> Ala, Lys492 --> Leu, Lys515 --> Ala, and Arg560 --> Glu. None of the mutations affected the low affinity activation by nucleotide of the phosphoenzyme-processing steps, indicating that modulatory nucleotide interacts differently from substrate nucleotide. Mutation Glu442 --> Ala greatly enhanced reaction of Lys515 with fluorescein isothiocyanate, indicating that the two residues form a salt link in the native protein.     

Serum concentrations of free amino acids in growing pigs exposed to diurnal heat stress fluctuations

In areas where the ambient temperature (AT) is above the thermo neutral (TN) zone of pigs, significant changes within a 24-h period occur, differently affecting the availability of amino acids (AA) within the same day. An experiment was conducted to analyze the serum concentrations (SC) of free AA in pigs exposed to diurnal variations in AT. Six pigs (27.1 ±1.3 kg body weight) implanted with a thermometer to register the body temperature (BT) at 15-min intervals were used. Blood samples were collected on the last 3 d of the 14-d study, at 0700 h (lowest AT), 1200 h (mild HS), and 1600 h (severe HS). The pigs received 1.2 kg/d of an AA-supplemented, wheat-soybean meal diet, in two equal meals (0700 and 1900 h). The AT and BT, recorded at 0700, 1200, and 1600 h was: 30.6, 38.6, 41.1 °C, and 38.2, 39.5, 40.3 °C, respectively. The BT was significantly correlated (P < 0.001) with the AT. The SC (μM/mL) of Ile, Lys, Met, Val, Ala, Asn, and Pro were higher (P ≤ 0.01); Arg, Phe, Glu, and Tyr tended to be higher (P ≤ 0.10); but Cys was lower (P < 0.05) at 1200 h than at 0700 h. Lys was higher, Cys and Tyr were lower (P < 0.05), and Ile and Val tended to be higher (P ≤ 0.10) at 1600 h than at 0700 h. Serum Arg, Ile, Phe, Ala, Asn, Gln, Pro, Ser, and Tyr were lower (P < 0.05), and Leu and Val tended to be lower at 1600 h than at 1200 h. These data demonstrate that AT directly alters the BT of pigs, and that diurnal variations in AT differently affect their SC and availability of AA for growth.     

Interaction of Aldehyde dehydrogenase with acetaminophen as examined by spectroscopies and molecular docking

The interaction of acetaminophen, a non-substrate anionic ligand, with Aldehyde Dehydrogenase was studied by fluorescence, UV–Vis absorption, and circular dichroism spectroscopies under simulated physiological conditions. The fluorescence spectra and data generated showed that acetaminophen binding to ALDH is purely dynamic quenching mechanism. The acetaminophen-ALDH is kinetically rapid reversible interaction with a binding constant, K_a, of 4.91×10³ L mol^?1. There was an existence of second binding site of ALDH for acetaminophen at saturating acetaminophen concentration. The binding sites were non-cooperative. The thermodynamic parameters obtained suggest that Van der Waal force and hydrogen bonding played a major role in the binding of acetaminophen to ALDH. The interaction caused perturbation of the ALDH structures with an obvious reduction in the α-helix. The binding distance of 4.43 nm was obtained between Acetaminophen and ALDH. Using Ficoll 400 as macro-viscosogen and glycerol as micro-viscosogen, Stoke-Einstein empirical plot demonstrated that acetaminophen-ALDH binding was diffusion controlled. Molecular docking showed the participation of some amino acids in the complex formation with ?5.3 kcal binding energy. With these, ALDH might not an excipient detoxifier of acetaminophen but could be involved in its pegylation/encapsulation.     

<Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis> Phosphoenolpyruvate Carboxykinase: The Relevance of Glu299 and Leu460 for Nucleotide Binding

A homology model of Saccharomyces cerevisiae phosphoenolpyruvate (PEP) carboxykinase (ATP + oxaloacetate ⇄ ADP + PEP + CO₂) in complex with its substrates shows that the isobutyl group of Leu460 is in close proximity to the adenine ring of the nucleotide, while the carboxyl group of Glu299 is within hydrogen-bonding distance of the ribose 2′OH. The Leu460Ala mutation caused three-fold and seven-fold increases in the K _m for ADPMn⁻ and ATPMn²⁻, respectively, while the Glu299Ala mutation had no effect. Binding studies showed losses of approximately 2 kcal mol⁻¹ in the nucleotide binding affinity due to the Leu460Ala mutation and no effect for the Glu299Ala mutation. PEP carboxykinase utilized 2′deoxyADP and 2′deoxyATP as substrates with kinetic and equilibrium dissociation constants very similar to those of ADP and ATP, respectively. These results show that the hydrophobic interaction between Leu460 and the adenine ring of the nucleotide significantly contributed to the nucleotide affinity of the enzyme. The 2′deoxy nucleotide studies and the lack of an effect of the Glu299Ala mutation in nucleotide binding suggest that the possible hydrogen bond contributed by Glu299 and the ribose 2′OH group may not be relevant for nucleotide binding.     

In vitro and in vivo ACE inhibitory of pistachio hydrolysates and in silico mechanism of identified peptide binding with ACE

The ACE inhibitory activity of pistachio (Pistacia vera L.) kernel's hydrolysates by gastrointestinal enzymes was studied. Results indicated that hydrolysate successively hydrolyzed by pepsin and trypsin, Pe–Tr–H, presented in vitro ACE inhibitory activity as IC₅₀ 0.87 ± 0.04 mg/ml. The Pe–Tr–H can in vivo decrease around 22 mmHg in systolic blood pressure (SBP) and 16 mmHg in the diastolic blood pressure (DBP) at 4 h after the oral administration, however the pistachio kernel powder can slightly lower SBP and DBP. The Pe–Tr–H with the highest activity was then separated by ultrafiltration membrane of 3 kDa, size exclusion chromatography on Sephadex G-15 and G-10 columns and reversed phase high-performance liquid chromatography (RP-HPLC) consecutively. A novel ACE inhibitory peptide, ACKEP, with the IC₅₀ value of 126 μM, was identified by MALDI–TOF/TOF system. ACKEP has the same C-terminal residue as Lisinopril and Enalapril, which plays a key role in binding with ACE. The binding mechanism was explored at a molecular basis by docking experiments, which revealed that seven residues from ACE active site (His383, His387, Glu384, Arg522, Asp358, Ala356 and Asn70) and two atoms of ACKEP (O5, H60) greatly contributed to the combinative stabilization.     

riDOM,a cell penetrating peptide. Interaction with phospholipid bilayers

Melittin is an amphipathic peptide which has received much attention as a model peptide for peptide–membrane interactions. It is however not suited as a transfection agent due to its cytolytic and toxicological effects. Retro-inverso-melittin, when covalently linked to the lipid 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (riDOM), eliminates these shortcomings. The interaction of riDOM with phospholipid membranes was investigated with circular dichroism (CD) spectroscopy, dynamic light scattering, ζ-potential measurements, and high-sensitivity isothermal titration calorimetry. riDOM forms cationic nanoparticles with a diameter of ~ 13 nm which are well soluble in water and bind with high affinity to DNA and lipid membranes. When dissolved in bilayer membranes, riDOM nanoparticles dissociate and form transient pores. riDOM-induced membrane leakiness is however much reduced compared to that of authentic melittin. The secondary structure of the ri-melittin is not changed when riDOM is transferred from water to the membrane and displays a large fraction of β-structure. The ³¹P NMR spectrum of the nanoparticle is however transformed into a typical bilayer spectrum. The Gibbs free energy of riDOM binding to bilayer membranes is − 8.0 to − 10.0 kcal/mol which corresponds to the partition energy of just one fatty acyl chain. Half of the hydrophobic surface of the riDOM lipid extension with its 2 oleic acyl chains is therefore involved in a lipid–peptide interaction. This packing arrangement guarantees a good solubility of riDOM both in the aqueous and in the membrane phase. The membrane binding enthalpy is small and riDOM binding is thus entropy-driven.     

Pyrrolidine analogs of GZ-793A: Synthesis and evaluation as inhibitors of the vesicular monoamine transporter-2 (VMAT2)

Central heterocyclic ring size reduction from piperidinyl to pyrrolidinyl in the vesicular monoamine transporter-2 (VMAT2) inhibitor GZ-793A and its analogs resulted in novel N-propane-1,2(R)-diol analogs 11a–i. These compounds were evaluated for their affinity for the dihydrotetrabenazine (DTBZ) binding site on VMAT2 and for their ability to inhibit vesicular dopamine (DA) uptake. The 4-difluoromethoxyphenethyl analog 11f was the most potent inhibitor of [³H]-DTBZ binding (K_i = 560 nM), with 15-fold greater affinity for this site than GZ-793A (K_i = 8.29 μM). Analog 11f also showed similar potency of inhibition of [³H]-DA uptake into vesicles (K_i = 45 nM) compared to that for GZ-793A (K_i = 29 nM). Thus, 11f represents a new water-soluble inhibitor of VMAT function.