Interaction of tRNA with Safranal, Crocetin, and Dimethylcrocetin

Saffron is the red dried stigmas of Crocus sativus L. flowers and used both as a spice and as a drug in traditional therapeutic. The biological activity of saffron in modern medicine is in development. Its numerous applications as an anti-oxidant and anti-cancer agent are due to its secondary metabolites and their derivatives (safranal, crocins, crocetin, dimethylcrocetin). The aim of this study was to examine the interaction of transfer RNA with safranal, crocetin, and dimethylcrocetin in aqueous solution at physiological conditions. Constant tRNA concentration (6.25 mM) and various drug/tRNA (phosphate) molar ratios of 1/48 to 1/8 were used. FT-IR and UV-Visible difference spectroscopic methods have been applied to determine the drug binding mode, the binding constants and the effects of drug complexation on the stability and conformation of tRNA duplex. External binding mode was observed for safranal crocetin and dimethylcrocetin, with overall binding constants K(safranal) = 6.8 (+/- 0.34) x 10(3) M(-1), K(CRT) = 1.4 (+/- 0.31) x 10(4) M(-1), and K(DMCRT) = 3.4 (+/- 0.30) x 10(4) M(-1). Transfer RNA remains in the A-family structure, upon safranal, crocetin and dimethylcrocetin complexation.     

An Overview of DNA and RNA Bindings to Antioxidant Flavonoids

In this report we are examining how the antioxidant flavonoids can prevent DNA damage and what mechanism of action is involved in the process. Flavonoids are strong antioxidants that prevent DNA damage. The anticancer and antiviral activities of these natural products are implicated in their mechanism of actions. We study the interactions of quercetin (que), kaempferol (kae), and delphinidin (del) with DNA and transfer RNA in aqueous solution at physiological conditions, using constant DNA or RNA concentration 6.25 mmol (phosphate) and various pigment/polynucleotide(phosphate) ratios of 1/65 to 1 (DNA) and 1/48 to 1/8 (tRNA). The structural analysis showed quercetin, kaempferol, and delphinidin intercalate DNA and RNA duplexes with minor external binding to the major or minor groove and the backbone phosphate group with overall binding constants for DNA adducts K _que = 7.25 (±0.65) × 10⁴ M⁻¹, K _kae = 3.60 (±0.33) × 10⁴ M^−1, and K _del = 1.66 (±0.25) × 10⁴ M⁻¹ and for tRNA adducts K _que = 4.80 (±0.50) × 10⁴ M⁻¹, K _kae = 4.65 (±0.45) × 10⁴ M^−1, and K _del = 9.47 (±0.70) × 10⁴ M⁻¹. The stability of adduct formation is in the order of del>que>kae for tRNA and que>kae>del for DNA. Low flavonoid concentration induces helical stabilization, whereas high pigment content causes helix opening. A partial B to A-DNA transition occurs at high drug concentration, while tRNA remains in A-family structure. The antioxidant activity of flavonoids changes in order delphinidin>quercetin>kaempferol. The results show intercalated flavonoids can make them strong antioxidants to protect DNA from harmful free radical reactions.     

DNA interaction with saffron's secondary metabolites safranal, crocetin, and dimethylcrocetin

Saffron comes from the dried red stigmas of the Crocus sativus L. flower. Except for its use in cooking and in traditional medicine, it has numerous applications as an antitoxic, antioxidant, and anticancer agent due to its secondary metabolites and their derivatives (safranal, crocins, crocetin, dimethylcrocetin). However, there has been no information on the interactions of these secondary metabolites with individual DNA at molecular level. This study was designed to examine the interaction of safranal, crocetin (CRT), and dimethylcrocetin (DMCRT) with calf-thymus DNA in aqueous solution at physiological conditions, using constant DNA concentration (6.25 mM) and various drug/DNA(phosphate) molar ratios from 1/48 to 1/2. FTIR and UV-visible difference spectroscopic methods are used to determine the drug binding sites, the binding constants, and the effects of carotenoids and safranal complexation on the stability and conformation of DNA duplex. Both intercalative and external binding modes were observed, with overall binding constants K(safranal) = 1.24 x 10(3) M(-1), K(CRT) = 6.2 x 10(3) M(-1) and K(DMCRT) = 1.85 x 10(5) M(-1) A partial B- to A-DNA transition occurs at high carotenoids and safranal concentrations.     

DNA Interaction with Naturally Occurring Antioxidant Flavonoids Quercetin,Kaempferol, and Delphinidin

Abstract

Flavonoids are strong antioxidants that prevent DNA damage. The anticancer and antiviral activities of these natural products are implicated in their mechanism of actions. However, there has been no information on the interactions of these antioxidants with individual DNA at molecular level. This study was designed to examine the interaction of quercetin (que), kaempferol (kae), and delphinidin (del) with calf-thymus DNA in aqueous solution at physiological conditions, using constant DNA concentration (6.5 mmol) and various drug/DNA(phosphate) ratios of 1/65 to 1. FTIR and UV-Visible difference spectroscopic methods are used to determine the drug binding sites, the binding constants and the effects of drug complexation on the stability and conformation of DNA duplex.

Structural analysis showed quercetin, kaempferol, and delphinidin bind weakly to adenine, guanine (major groove), and thymine (minor groove) bases, as well as to the backbone phosphate group with overall binding constants Kque = 7.25 × 10⁴M^?1, Kkae = 3.60 × 10⁴M^?1, and Kdel = 1.66 × 10⁴M^?1. The stability of adduct formation is in the order of que>kae>del. Delphinidin with a positive charge induces more stabilizing effect on DNA duplex than quercetin and kaempferol. A partial B to A-DNA transition occurs at high drug concentrations.     

Complexes of antiparallel telomeric G-quadruplex d(TTAGGG)4 with carboxymethyl tetracationic porphyrins

Porphyrins are a chemical class that is widely used in drug design. Cationic porphyrins may bind to DNA guanine quadruplexes. We report the parameters of the binding of 5,10,15,20-tetrakis(N-carboxymethyl-4-pyridinium) porphyrin (P1) and 5,10,15,20-tetrakis(N-etoxycarbonylmethyl-4-pyridinium) porphyrin (P2) to antiparallel telomeric G-quadruplex formed by d(TTAGGG)₄ sequence (TelQ). The binding constants (K _i ) and the number of binding sites (N _j ) were determined from absorption isotherms generated from the absorption spectra of complexes of P1 and P2 with TelQ. Compound P1 demonstrated a high affinity to TelQ (K _i = (40 ± 6) × 10⁶ M^?1, N ₁ = 1; K ₂ = (5.4 ± 0.4) × 10⁶ M^?1, N ₂ = 2). In contrast, the binding constants of P2-TelQ complexes (K ₁ = (3.1 ± 0.2) × 10⁶ M^?1, N ₁ = 1; K ₂ = (1.2 ± 0.2) × 10⁶ M^?1, N ₂ = 2) were one order of magnitude smaller than the corresponding values for P2-TelQ complexes. Measurements of the quantum yield and fluorescence lifetime of the drug’s TelQ complexes revealed two types of binding sites for P1 and P2 on the quadruplex oligonucleotide. We concluded that strong complexes can result from the interaction of the porphyrins with TTA loops whereas the weaker complexes are formed with G-quartets. The altered TelQ conformation detected by the circular dichroism spectra of P1-TelQ complexes can be explained by the disruption of the G-quartet. We conclude that peripheral carboxy groups contribute to the high affinity of P1 for the antiparallel telomeric G-quadruplex.     

Synthesis,Chemical Characterization,DNA Binding,Antioxidant, Antibacterial,and Antifungal Activities of Ferrocence Incorporated Selenoureas

Ferrocene‐incorporated selenoureas 1‐(4‐methoxybenzoyl)‐3‐(4‐ferrocenylphenyl)selenourea (P4Me), 1‐(3‐methoxybenzoyl)‐3‐(4‐ferrocenylphenyl)selenourea (P3Me), and 1‐(2‐methoxybenzoyl)‐3‐(4‐ferrocenylphenyl)selenourea (P2Me) were synthesized and characterized by nuclear magnetic resonance, Fourier transform infrared spectroscopy, atomic absorption spectroscopy, CHNS, and single‐crystal X‐ray diffraction. DNA interaction of the compounds was investigated with cyclic voltammetry, UV–visible spectroscopy, and viscometry, which is a prerequisite for anticancer agents. Drug‐DNA binding constant was found to vary in the sequence: K_P4Me (4.9000 × 10⁴ M^?1) > K_P2Me (2.318 × 10⁴ M^?1) > K_P3Me (1.296 × 10⁴ M^?1). Antioxidant (1,1‐diphenyl‐2‐picrylhydrazyl), antifungal (against Faussarium solani and Helmentosporium sativum), and antibacterial (against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Bacillus subtilis) activities have also been reported in addition.     

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.     

Probing the binding sites of resveratrol,genistein, and curcumin with milk β-lactoglobulin

We determined the binding sites of curcumin (cur), resveratrol (res), and genistein (gen) with milk β-lactoglobulin (β-LG) at physiological conditions. Fourier transform infrared spectroscopy, circular dichroism, and fluorescence spectroscopic methods as well as molecular modeling were used to determine the binding of polyphenol–protein complexes. Structural analysis showed that polyphenols bind β-LG via both hydrophilic and hydrophobic contacts with overall binding constants of K_{curcumin–β-LG}?=?4.4 (±?.4)?×?10⁴ M^?1, K_{resveratrol–β-LG}?=?4.2 (±?.2)?×?10⁴ M^?1, and K_{genistein–β-LG}?=?1.2 (±?.2)?×?10⁴?M^?1. The number of polyphenol molecules bound per protein (n) was 1 (cur), 1.1 (res), and 1 (gen). Molecular modeling showed the participation of several amino acid residues in polyphenol–protein complexation with the free binding energy of ?12.67 (curcumin–β-LG), ?12.60 (resveratrol–β-LG), and ?10.68?kcal/mol (genistein–β-LG). The order of binding was cur?>?res?>?gen. Alteration of the protein conformation was observed in the presence of polyphenol with a major reduction of β-sheet and an increase in turn structure, causing a partial protein structural destabilization. β-LG might act as a carrier to transport polyphenol in vitro.     

The interaction of beta-lactoglobulin with ciprofloxacin and kanamycin; a spectroscopic and molecular modeling approach

A vast research has been conducted to find suitable and safe carriers for vital and pH-sensitive drugs including antibiotics. This article reports the use of easily accessible and abundant purified beta-lactoglobulin (β-LG) protein as the potential carrier of widely used Kanamycin (Kana) and Ciprofloxacin (Cip) antibiotics. Spectroscopic techniques (Fluorescence, UV–vis, Circular Dichroism) combined with molecular docking were used to determine the binding mechanism of these drugs. Fluorescence studies showed moderate binding affinity with the calculated binding constants K_Cip = 60.1 (±0.2)?×?10³ M^?1 and K_kana = 2.5 (±0.6)?×?10³ M^?1 with the order of Cip > Kana. Results of UV–vis were consistent with fluorescence measurements and demonstrated a stronger complexation for Cip rather than Kana. The secondary structure of β-LG was preserved upon interaction with Kana; however, a reduction in β-sheet content from 39.1 to 31.9% was convoyed with an increase in α-helix from 12.8 to 20.5% due to complexation of Cip. Molecular docking studies demonstrated that preferred binding sites of these drugs are not the same and several amino acids are involved in stabilizing the interaction. Based on the achieved results, Kana and Cip can spontaneously bind to β-LG and this protein may serve as their transport vehicle.     

An investigation into the altered binding mode of green tea polyphenols with human serum albumin on complexation with copper

Green tea is rich in several polyphenols, such as (?)-epicatechin-3-gallate (ECG), (?)-epigallocatechin (EGC), and (?)-epigallocatechin-3-gallate (EGCG). The biological importance of these polyphenols led us to study the major polyphenol EGCG with human serum albumin (HSA) in an earlier study. In this report, we have compared the binding of ECG, EGC, and EGCG and the Cu(II) complexes of EGCG and ECG with HSA. We observe that the gallate moiety of the polyphenols plays a crucial role in determining the mode of interaction with HSA. The binding constants obtained for the different systems are 5.86?±?0.72?×?10⁴ M^?1 (K _ECG-HSA), 4.22?±?0.15?×?10⁴ M^?1 (K _{ECG-Cu(II)-HSA}), and 9.51?±?0.31?×?10⁴ M^?1 (K _{EGCG-Cu(II)-HSA}) at 293?K. Thermodynamic parameters thus obtained suggest that apart from an initial hydrophobic association, van der Waals interactions and hydrogen bonding are the major interactions which held together the polyphenols and HSA. However, thermodynamic parameters obtained from the interactions of the copper complexes with HSA are indicative of the involvement of the hydrophobic forces. Circular dichroism and the Fourier transform infrared spectroscopic measurements reveal changes in α-helical content of HSA after binding with the ligands. Data obtained by fluorescence spectroscopy, displacement experiments along with the docking studies suggested that the ligands bind to the residues located in site 1 (subdomains IIA), whereas EGC, that lacks the gallate moiety, binds to the other hydrophobic site 2 (subdomain IIIA) of the protein.     

Investigation of binding mechanism of novel 8-substituted coumarin derivatives with human serum albumin and α-1-glycoprotein

Coumarin molecules have biological activities possessing lipid-controlling activity, anti-hepatitis C activity, anti-diabetic, anti-Parkinson activity, and anti-cancer activity. Here, we have presented an inclusive study on the interaction of 8-substituted-7-hydroxy coumarin derivatives (Umb-1/Umb-2) with α-1-glycoprotein (AGP) and human serum albumin (HSA) which are the major carrier proteins in the human blood plasma. Binding constants obtained from fluorescence emission data were found to be K_Umb-1=3.1 ± .01 × 10⁴ M^?1, K_Umb-2 = 7 ± .01 × 10⁴ M^?1, which corresponds to ?6.1 and ?6.5 kcal/mol of free energy for Umb-1 and Umb-2, respectively, suggesting that these derivatives bind strongly to HSA. Also these molecules bind to AGP with binding constants of K_Umb-1-AGP=3.1 ± .01 × 10³ M^?1 and K_Umb-2-AGP = 4.6 ± .01 × 10³ M^?1. Further, the distance, r between the donor (HSA) and acceptor (Umb-1/Umb-2) was calculated based on the Forster’s theory of non-radiation energy transfer and the values were observed to be 1.14 and 1.29 nm in Umb-1–HSA and Umb-2–HSA system, respectively. The protein secondary structure of HSA was partially unfolded upon binding of Umb-1 and Umb-2. Furthermore, site displacement experiments with lidocaine, phenylbutazone (IIA), and ibuprofen (IIIA) proves that Umb derivatives significantly bind to subdomain IIIA of HSA which is further supported by docking studies. Furthermore, Umb-1 binds to LYS402 with one hydrogen bond distance of 2.8 Å and Umb-2 binds to GLU354 with one hydrogen bond at a distance of 2.0 Å. Moreover, these molecules are stabilized by hydrophobic interactions and hydrogen bond between the hydroxyl groups of carbon-3 of coumarin derivatives.     

Enhanced Expression of an Endothelin ETA Receptor in Capillaries from Human Glioblastoma: A Quantitative Receptor Autoradiographic Analysis Using a Radioluminographic Imaging Plate System

Abstract: We identified and characterized ¹²⁵I-endothelin-1 (¹²⁵I-ET-1) binding sites in tumor capillaries isolated from human glioblastomas, using the quantitative receptor autoradiographic technique with pellet sections. Quantification was done using the computerized radioluminographic imaging plate system. High-affinity ET receptors were localized in capillaries from glioblastomas and the surrounding brain tissues (K_D = 4.7 ± 1.0 × 10^?10 and 1.6 ± 0.3 × 10^?10M, respectively; B_max = 161 ± 38 and 140 ± 37 fmol/mg, respectively; mean ± SEM, n = 5). BQ-123, a selective antagonist for the ET_A receptor, potently competed for ¹²⁵I-ET-1 binding to sections of the microvessels with IC₅₀ values of 5.1 ± 0.3 and 5.1 ± 1.5 nM, and 10^?6M BQ-123 displaced 84 and 58% of ET binding to capillaries from tumors and brains, respectively. In addition, competition curves obtained in the presence of increasing concentrations of ET-3 showed two components (IC₅₀ = 5.7 ± 2.5 × 10^?10 and 1.4 ± 0.2 × 10^?6M for tumor microvessels, 1.8 ± 0.6 × 10^?10 and 1.1 ± 0.3 × 10^?6M for brain microvessels, respectively). Our results indicate that (a) the method we used is simple and highly sensitive for detecting and characterizing various receptors in tumor capillaries, especially in the case of a sparse specimen, and (b) capillaries in glioblastomas express specific high-affinity ET binding sites, candidates for biologically active ET receptors, which predominantly belong to the ET_A subtype.     

The optical biosensor study of the redox partner interaction with the cytochrome P450 2B4-containing monooxygenase system under hydroxylation conditions

The interactions between cytochrome P450 2B4 (d-2B4), NADPH:cytochrome P450 reductase and cytochrome b5 have been investigated in the monomeric reconstituted P450 2B4-containing monooxygenase system in the presence of a substrate (7-pentoxyresorufin) and an electron donor, NADPH. Each partner was immobilized via its amino groups on the carboxymethyldextran biochip surface of the optical biosensor IAsys+. Such mode immobilization was not accompanied by any loss of activities of the immobilized proteins. The formation of binary d-Fp/d-2B4 complexes was registered. The association/dissociation rate constants (k_on/k_off) were (0.013 ± 0.005) × 10⁶ M^?1 s^?1/0.05 ± 0.02 s^?1, and dissociation constant (K_D) was (0.26 ± 0.13) × 10^?6 M. Comparison of k_on, k_off and K_D values for d-Fp/d-2B4 complexes formed under hydroxylation (O-dealkylation) with corresponding constants obtained for the oxidized proteins of (0.10 ± 0.03) × 10⁶ M^?1 s^?1/(0.14 ± 0.06) s^?1, and (0.71 ± 0.37) × 10^?6 M, respectively shows that the decrease in k_on and an insignificant decrease in K_D are associated with the increase of complex lifetime during transition from the oxidized to hydroxylation conditions. Complex formation between d-Fp and d-b5 was not registered in both hydroxylation conditions and in the case of oxidized forms of these proteins. In both cases formation of the ternary d-Fp/d-2B4/d-b5 complexes occurred.     

Equilibrium dialysis binding studies of 1,N6-ethenoadenosine diphosphate (epsilon ADP) to myosin, heavy meromyosin, and subfragment one

The binding of the fluorescent analog of adenosine diphosphate (ADP)¹, 1,N⁶-ethenoadenosine diphosphate (εADP) to myosin and its subfragments, heavy meromyosin (HMM) and subfragment one (S1), has been studied under analagous conditions to those previously used in comparable studies on the binding of ADP to these molecules. The results indicate that there are two binding sites for εADP on myosin and HMM, and one site on S1. The dissociation constants for all had an identical value, within experimental error, of 2.0 (^± .5) × 10^?5 M^?1. This is identical to the values found by Young (J. Biol. Chem., $\text{242}$, 2790 (1967)) for ADP. In addition, the kinetics of hydrolysis of εATP versus ATP by S1 were studied. Values of V_max and K_m were 25 μM phosphate sec^?1 (gm protein)^?1 and 5 × 10^?5 M^?1 for ATP, and 80 μN phosphate sec^?1 (gm protein)^?1 and 45 × 10^?5 M^?1 for εATP. The results indicate that the increased V_max that occurs when εATP is used as a substitute for ATP is not due to either an increased binding affinity of ATP for myosin and its subfragments, nor due to a decreased binding affinity of εATP versus ADP. This in turn suggests that the increase in V_max may be due to an increased hydrolytic rate of εATP vs ATP in the enzyme substrate complex.     

Revised model of calcium and magnesium binding to the bacterial cell wall

Metals bind to the bacterial cell wall, yet the binding mechanisms and affinity constants are not fully understood. The cell wall of gram positive bacteria is characterized by a thick layer of peptidoglycan and anionic teichoic acids anchored in the cytoplasmic membrane as lipoteichoic acid or covalently bound to the cell wall as wall teichoic acid. The polyphosphate groups of teichoic acid provide one-half of the metal binding sites for calcium and magnesium, which contradicts previous reports that calcium binding is 100 % dependent on teichoic acid. The remaining binding sites are formed with the carboxyl units of peptidoglycan. In this work we report equilibrium association constants and total metal binding capacities for the interaction of calcium and magnesium ions with the bacterial cell wall. Metal binding is much stronger than previously reported. Curvature of Scatchard plots from the binding data and the resulting two regions of binding affinity suggest the presence of negative cooperative binding, which means that the binding affinity decreases as more ions become bound to the sample. For Ca²⁺, Region I has a K_A = (1.0 ± 0.2) × 10⁶ M^?1 and Region II has a K_A = (0.075 ± 0.058) × 10⁶ M^?1. For Mg²⁺, K_A1 = (1.5 ± 0.1) × 10⁶ and K_A2 = (0.17 ± 0.10) × 10⁶. A binding capacity (η) is reported for both regions. However, since binding is still occurring in Region II, the total binding capacity is denoted by η₂, which are 0.70 ± 0.04 and 0.67 ± 0.03 µmol/mg for Ca²⁺ and Mg²⁺ respectively. These data contradict the current paradigm of only a single metal affinity value that is constant over a range of concentrations. We also find that measurement of equilibrium binding constants is highly sample dependent. This suggests a role for diffusion of metals through heterogeneous cell wall fragments. As a result, we are able to reconcile many contradictory theories that describe binding affinity and the binding mode of divalent metal cations.     

Kinetics of Ni(II) and Co(II) monocomplex formation with O-phospho-dl-serine

The complexation reactions of O-phospho-DL-serine with Ni(II) or Co(II) were studied at 25°C and ionic strength 0.2 M (KNO₃) by temperature-jump. The observed rate constants for formation of the Ni²⁺ and Co⁺² monocomplexes were (1.32 ± 0.09) × 10⁵ and (1.73 ± 0.33) × 10⁷ M^?1 sec^?1, respectively. Complexation is postulated to involve formation of a monocoordinated steady state intermediate followed by rate-determining chelate ring closure.     

Properties of [3H]diazepam binding sites on rat blood platelets

Intact rat blood platelets are shown to possess benzodiazepine binding sites of the peripheral type, binding of [³H]diazepam being strongly inhibited by Ro5-4864 (K_i = 3.6 ± 0.5 nM) but only weakly inhibited by clonazepam (K_i = 35.1 ± 18.2 μM). Binding of [³H]diazepam is specific and saturable. Scatchard analysis reveals a single class of binding sites with K_D = 14.7 ± 1.0 nM and B_max = 564 ± 75 fmoles/10⁸ platelets. The Hill coefficient is 0.94, indicating a lack of binding site heterogeneity or negative cooperativity. Binding reaches equiliibrium at 6 min, with k₊₁ = 2.9 × 10⁷ M^?1 min^?1, and is rapidly reversible ($\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext><mtext>\; =\; 2.2\; </mtext><mtext>min</mtext>}}$ with K_?1 = 0.315 min^?1. K_D derived from the rate constants agrees with that estimated by Scatchard analysis. K_D of the crude membrane fraction of platelets is also close to that of intact platelets. Binding of [³H]diazepam is linear with platelet number (between 0.25–2 × 10⁸ platelets), is temperature sensitive with maximum binding at 0°C, and has a broad optimal pH range between pH 5–9.     

Differential interactions and structural stability of chitosan oligomers with human serum albumin and α-1-glycoprotein

Chitosan is a naturally occurring deacetylated derivative of chitin with versatile biological activities. Here, we studied the interaction of chitosan oligomers with low degree of polymerization such as chitosan monomer (CM), chitosan dimer (CD), and chitosan trimer (CT) with human serum albumin (HSA) a major blood carrier protein and α-1-glycoprotein (AGP). Since, HSA and AGP are the two important plasma proteins that determine the drug disposition and affect the fate of distribution of drugs. Fluorescence emission spectra indicated that CM, CD, and CT had binding constants of K_CM = 6.2 ± .01 × 10⁵ M^?1, K_CD = 5.0 ± .01 × 10⁴ M^?1, and K_CT = 1.6 ± .01 × 10⁶ M^?1_, respectively, suggesting strong binding with HSA. However, binding of chitooligomers with AGP was insignificant. Thermodynamic and molecular docking analysis indicated that hydrogen bonds and also hydrophobic interaction played an important role in stabilizing the HSA-chitooligomer complexes with free energies of ?7.87, ?6.35, and ?8.4?Kcal/mol for CM, CD, and CT, respectively. Further, circular dichroism studies indicated a minor unfolding of HSA secondary structure, upon interaction with chitooligomers, which are supported with fluctuations of root mean square deviation (RMSD) and radius of gyration (R_g) of HSA. Docking analysis revealed that all three chitooligomers were bound to HSA within subdomain IIA (Site I). In addition, RMSD and R_g analysis depicted that HSA-chitooligomer complexes stabilized at around 4.5 ns. These results suggest that HSA might serve as a carrier in delivering chitooligomers to target tissues than AGP which has pharmacological importance.     

Structural characterization of cationic lipid–tRNA complexes

Despite considerable interest and investigations on cationic lipid–DNA complexes, reports on lipid–RNA interaction are very limited. In contrast to lipid–DNA complexes where lipid binding induces partial B to A and B to C conformational changes, lipid–tRNA complexation preserves tRNA folded state. This study is the first attempt to investigate the binding of cationic lipid with transfer RNA and the effect of lipid complexation on tRNA aggregation and condensation. We examine the interaction of tRNA with cholesterol (Chol), 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP), dioctadecyldimethylammoniumbromide (DDAB) and dioleoylphosphatidylethanolamine (DOPE), at physiological condition, using constant tRNA concentration and various lipid contents. FTIR, UV-visible, CD spectroscopic methods and atomic force microscopy (AFM) were used to analyze lipid binding site, the binding constant and the effects of lipid interaction on tRNA stability, conformation and condensation. Structural analysis showed lipid–tRNA interactions with G–C and A–U base pairs as well as the backbone phosphate group with overall binding constants of K_Chol = 5.94 (± 0.8) × 10⁴ M^–1, K_DDAB = 8.33 (± 0.90) × 10⁵ M^–1, K_DOTAP = 1.05 (± 0.30) × 10⁵ M^–1 and K_DOPE = 2.75 (± 0.50) × 10⁴ M^–1. The order of stability of lipid–tRNA complexation is DDAB > DOTAP > Chol > DOPE. Hydrophobic interactions between lipid aliphatic tails and tRNA were observed. RNA remains in A-family structure, while biopolymer aggregation and condensation occurred at high lipid concentrations.