Retinol and retinoic acid bind human serum albumin: stability and structural features

Vitamin A components, retinol and retinoic acid, are fat-soluble micronutrients and critical for many biological processes, including vision, reproduction, growth, and regulation of cell proliferation and differentiation. The cellular uptake of Vitamin A is through specific interaction of a plasma membrane receptor with serum retinol-binding protein. Human serum albumin (HSA), as a transport protein, is the major target of several micronutrients in vivo. The aim of present study was to examine the interaction of retinol and retinoic acid with human serum albumin in aqueous solution at physiological conditions using constant protein concentration and various retinoid contents. FTIR, UV–vis, CD and fluorescence spectroscopic methods were used to determine retinoid binding mode, the binding constant and the effects of complexation on protein secondary structure.

Structural analysis showed that retinol and retinoic acid bind non-specifically (H-bonding) via protein polar groups with binding constants of K_ret = 1.32 (±0.30) × 10⁵ M⁻¹ and K_retac = 3.33 (±0.35) × 10⁵ M⁻¹. The protein secondary structure showed no alterations at low retinoid concentrations (0.125 mM), whereas at high retinoid content (1 mM), an increase of -helix from 55% (free HSA) to 60% and a decrease of β-sheet from 22% (free HSA) to 18% occurred in the retinoid–HSA complexes. The results point to a partial stabilization of protein secondary structure at high retinoid content.     

Locating the binding sites of retinol and retinoic acid with milk β-lactoglobulin

β-lactoglobulin (β-LG) is a member of lipocalin superfamily of transporters for small hydrophobic molecules such as retinoids. We located the binding sites of retinol and retinoic acid on β-LG in aqueous solution at physiological conditions, using FTIR, CD, fluorescence spectroscopic methods, and molecular modeling. The retinoid-binding sites and the binding constants as well as the effect of retinol and retinoic acid complexation on protein stability and secondary structure were determined. Structural analysis showed that retinoids bind strongly to β-LG via both hydrophilic and hydrophobic contacts with overall binding constants of K (retinol-) (β) (-LG?)=?6.4 (±?.6)?×?10(6)?M(-1) and K (retinoic acid-) (β) (-LG?)=?3.3 (±?.5)?×?10(6)?M(-1). The number of retinoid molecules bound per protein (n) is 1.1 (±?.2) for retinol and 1.5 (±?.3) for retinoic acid. Molecular modeling showed the participation of several amino acids in the retinoid-protein complexes with the free binding energy of -8.11?kcal/mol for retinol and -7.62?kcal/mol for retinoic acid. Protein conformation was altered with reduction of β-sheet from 59 (free protein) to 52-51% and a major increase in turn structure from 13 (free protein) to 24-22%, in the retinoid-β-LG complexes, indicating a partial protein destabilization.     

Structure and Dynamics of Ligand-Template Interactions of Topoisomerase Inhibitory Analogs of Hoechst 33258: High Field 1H-NMR and Restrained Molecular Mechanics Studies

Abstract

The binding characteristics of Hoechst 33258 (1), a synthetic bis-benzimidazole, and its structural analog 2, with one of the benzimidazoles replaced by a pyridoimidazole, to the self-complementary decadeoxyribonucleotide sequences d(CGCAATTGCG)² (A) and d-(CATGGCCATG)₂ (B) respectively, were examined using high field ¹H-NMR techniques. Selective complexation induced chemical shift changes, the presence of exchange signals and intermolecular NOE contacts between the ligands and the minor groove protons of the oligonucleotides suggest the preferred binding sites as the centrally located AATT segment for complex Al, and the CCAT segment for complex B2. The B-type conformations of the two DNA duplexes are preserved upon complexation, as confirmed by the 2D-NOESY based sequential connectivities involving DNA base and sugar protons. Close intermolecular NOE based contacts between the ligands and their respective DNA sequences were further refined to model the ligand-DNA complexes starting from the computer generated B-type structures for the oligonucleotides. Force field calculations of ligand-DNA interaction energies indicate a more favorable contribution from the van der Waals energy component in the case of complex Al consistent with its stronger net binding compared with the complex B2.

Overall, the incorporation of a pyridinic nitrogen in Hoechst 33258 structure alters its selectivity for base pair recognition from AT to G.C, resulting largely from the formation of a hydrogen bond between the new basic center and the 2-NH₂ group of a guanosine moiety. The rates for the exchange of ligands between the two equivalent binding sites (AATT for 1, and CCAT for 2) of the self-complementary DNA sequences, are estimated from analyses of coalescence of NMR signals to be 189 _s ^?1 at 301K for A1, and 79_s ^?1 at 297 K for B2; which correspond to ΔG? of 13.8 and 18.6 kcal.mol^?1 respectively.     

Locating the binding sites of retinol and retinoic acid with milk β-lactoglobulin

β-lactoglobulin (β-LG) is a member of lipocalin superfamily of transporters for small hydrophobic molecules such as retinoids. We located the binding sites of retinol and retinoic acid on β-LG in aqueous solution at physiological conditions, using FTIR, CD, fluorescence spectroscopic methods, and molecular modeling. The retinoid-binding sites and the binding constants as well as the effect of retinol and retinoic acid complexation on protein stability and secondary structure were determined. Structural analysis showed that retinoids bind strongly to β-LG via both hydrophilic and hydrophobic contacts with overall binding constants of K _{retinol- β -LG?}=?6.4 (±?.6)?×?10⁶?M^?1 and K _{retinoic acid- β -LG?}=?3.3 (±?.5)?×?10⁶?M^?1. The number of retinoid molecules bound per protein (n) is 1.1 (±?.2) for retinol and 1.5 (±?.3) for retinoic acid. Molecular modeling showed the participation of several amino acids in the retinoid–protein complexes with the free binding energy of ?8.11?kcal/mol for retinol and ?7.62?kcal/mol for retinoic acid. Protein conformation was altered with reduction of β-sheet from 59 (free protein) to 52–51% and a major increase in turn structure from 13 (free protein) to 24–22%, in the retinoid–β-LG complexes, indicating a partial protein destabilization.     

Structural studies on ligand–DNA systems: A robust approach in drug design

Molecular docking, molecular mechanics, molecular dynamics and relaxation matrix simulation protocols have been extensively used to generate the structural details of ligand-receptor complexes in order to understand the binding interactions between the two entities. Experimental methods like NMR spectroscopy and X-ray crystallography are known to provide structural information about ligand-receptor complexes. In addition, fluorescence spectroscopy, circular dichroism (CD) spectroscopy and molecular docking have also been utilized to decode the phenomenon of the ligand-DNA interactions, with good correlation between experimental and computational results. The DNA binding affinity was demonstrated by analysing fluorescence spectral data. Structural rigidity of DNA upon ligand binding was identified by CD spectroscopy. Docking is carried out using the DNA-Dock program which results in the binding affinity data along with structural information like interatomic distances and H-bonding, etc. The complete structural analyses of various drug-DNA complexes have afforded results that indicate a specific DNA binding pattern of these ligands. It also exhibited that certain structural features of ligands can make a ligand to be AT- or GC-specific. It was also demonstrated that changing specificity from AT base pairs to GC base pairs further improved the DNA topoisomerase inhibiting activity in certain ligands. Thus, a specific molecular recognition signature encrypted in the structure of ligand can be decoded and can be effectively employed in designing more potent antiviral and antitumour agents.     

Candenatenins G–K,phenolic compounds from Dalbergia candenatensis heartwood

Five new phenolic compounds, designated candenatenins G–K (1–5), along with four known compounds, were isolated from the heartwood of Dalbergia candenatensis. The structures of these compounds were elucidated by HR-EI-MS, ¹H and ¹³C NMR, COSY, HMQC, HMBC, and NOESY spectra. Compound 5 exhibited potent activity against DPPH radical scavenging with IC₅₀ value of 25.7 μM, whereas compound 2 showed cytotoxicity against NCI-H187 cell line with IC₅₀ value of 14.8 μM.     

Cytotoxic cardenolide glycoside from the seeds of Cerbera odollam

A cardenolide glycoside, 3 beta-O-(2'-O-acetyl-l- thevetosyl)-15(14-->8)-abeo-5 beta-(8R)-14-oxo-card-20(22)-enolide (2'-O-acetyl cerleaside A), was isolated from a methylene chloride extract of the seeds of Cerbera odollam, together with four known compounds: cerleaside A, 17 alpha-neriifolin, 17 beta- neriifolin and cerberin. Their structures were elucidated by spectroscopic methods. All compounds except cerleaside A exhibited cytotoxic activities against oral human epidermoid carcinoma (KB), human breast cancer cell (BC) and human small cell lung cancer (NCI-H187).     

Conventional and exergetic life cycle assessment of organic rankine cycle implementation to municipal waste management: the case study of Mae Hong Son (Thailand)

Purpose

The critical issue of waste management in Thailand has been rapidly increasing in almost all of the cities due to the economic growth and rising population that could double the amount of solid waste in landfill area. The alternative ways of waste treatment that have more efficiency and effectiveness in terms of energy, ecology, and resources become the key issue for each municipality to replace the old fashioned technology and be able to enhance the ability of solid waste problem management. Waste to energy is one of the favorable approaches to diminish the amount of waste to landfill and utilize waste for electricity. The aim of this study is to identify and quantify the life cycle impacts of the municipal solid waste (MSW) of Mae Hong Son municipality (MHSM), and the case study is the selected waste treatment technology of the Refuse-Derived Fuel (RDF) hybrid with 20 kW of Organic Rankine Cycle (ORC).

Methods

The functional unit is defined as 1 t of MSW. The energy, environment, and resource impacts were evaluated by using Life Cycle Assessment (LCA); ReCipe and Net Energy Consumption were referred to calculate the environmental impacts and the benefits of energy recovery of WtE technology. Exergetic LCA was used to analyze the resource consumption, especially land use change.

Results and discussion

The results indicated that the environmental impacts were comparatively high at the operation stage of RDF combustion. On the other hand, the production stage of RDF illustrated the highest energy consumption. The ORC power generation mainly consumed resources from material and energy used. The ORC system demonstrated better results in terms of energy and resource consumption when applied to waste management, especially the land required for landfill. Substitution of electricity production from ORC system was the contributor to the reduction of both energy and resource consumption. Installation of spray dry and fabric filter unit to RDF burner can reduce heavy metals and some pollutants leading to the reduction of most of the impacts such as climate change, human toxicity, and fossil depletion which are much lower than the conventional landfill.

Conclusions

LCA results revealed that the environmental impacts and energy consumption can be reduced by applying the RDF and ORC systems. The exergetic LCA is one of the appropriate tools used to evaluate the resource consumption of MSW. It is obviously proven that landfill contributed to higher impacts than WtE for waste management.

     

Glycopentaphyllone: The first isolation of hydroperoxyquinolone from the fruits of Glycosmis pentaphylla

A new hydroperoxyquinolone alkaloid, glycopentaphyllone (1), along with nine compounds (2–10), was isolated from the fruits of Glycosmis pentaphylla. Their structures were elucidated on the basis of spectroscopic methods. The absolute configuration of glycopentaphyllone at C-2′ was established as S-configuration by applying Mosher's method. In addition, the completed assignments of ¹³C NMR as well as 2D NMR spectral data of compound 5 were reported herein for the first time. Also, all isolates were evaluated for antibacterial activity against Escherichia coli TISTR 780, Salmonella typhimurium TISTR 292, Staphylococcus aureus TISTR 1466, and Methicillin-resistant S. aureus SK1.     

Carbazole alkaloids and coumarins from Clausena lansium roots

Two new carbazole alkaloids, mafaicheenamines D (1) and E (2), together with twelve known compounds (3–14) were isolated from the roots of Clausena lansium. Spectroscopic methods, including NMR, UV, IR, and MS spectral data were used for structural characterization. Some of isolates were evaluated for their cytotoxicity against three human cancer cell lines (KB, MCF-7, and NCI-H187).