Intermolecular interactions of lysobisphosphatidic acid with phosphatidylcholine in mixed bilayers

Lysobisphosphatidic acid (LBPA) can be regarded to represent a unique derivative of phosphatidylglycerol. This lipid is highly enriched in late endosomes where it can comprise up to 10-15 mol% of all lipids and in these membranes, LBPA appears to be segregated into microdomains. We studied the thermotropic behavior of pure dioleoyl-LBPA mono- and bilayers using Langmuir-lipid monolayers, electron microscopy, differential scanning calorimetry (DSC), and fluorescence spectroscopy. LBPA formed metastable, liquid-expanded monolayers at an air/buffer interface, and its compression isotherms lacked any indication for structural phase transitions. Neat LBPA formed multilamellar vesicles with no structural transitions or phase transitions between 10 and 80 degrees C at a pH range of 3.0-7.4. We then proceeded to study mixed LBPA/dipalmitoylphosphatidylcholine (DPPC) bilayers by DSC and fluorescence spectroscopy. Incorporating increasing amounts of LBPA (up to X(LBPA) (molar fraction)=0.10) decreased the co-operativity of the main transition for DPPC, and a decrease in the main phase transition as well as pretransition temperature of DPPC was observed yet with no effect on the enthalpy of this transition. In keeping with the DSC data for DPPC, 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC)/LBPA mixed bilayers were more fluid, and no evidence for lateral phase segregation was observed. These results were confirmed using fluorescence microscopy of Langmuir-lipid films composed of POPC and LBPA up to X(LBPA)=0.50 with no evidence for lateral phase separation. As late endosomes are eminently acidic, we examined the effect of lowering pH on lateral organization of mixed PC/LBPA bilayers by DSC and fluorescence spectroscopy. Even at pH 3.0, we find no evidence of LBPA-induced microdomain formation at LBPA contents found in cellular organelles.     

Co (II), Ni(II) and Cu(II) complexes with a new pendant armed macrocyclic ligand showing several π,π-interactions

A new ligand, L, bearing four cyanoethyl pendant groups has been synthesized by reaction of the precursor ligand L¹ with acrylonitrile. The X-ray crystal structure of ligand L reveals the presence of a nanotubular structure in the solid state connected by intermolecular π,π-stacking interactions between adjacent pyridine rings. The coordination capability towards transition metal ions [Co(II), Ni(II) and Cu(II)] has been investigated starting from the hydrated nitrate and perchlorate salts of the metals. The new ligand L and the metal complexes obtained were characterized by elemental analysis, FAB MS, conductivity measurements, magnetic studies, IR and UV-vis spectroscopy. Furthermore, the crystal structure of ligand L and of the complexes [CoL][Co(NO₃)₄] · CH₃CN (1), [NiL](NO₃)₂ (3), [NiL](ClO₄)₂ · CH₃CN · 3H₂O (4), [CuL][Cu(NO₃)₃(H₂O)₂](NO₃) · H₂O (5) and [CuL](ClO₄)₂ · 2CH₃CN (6) were determined. The nitrate ions in the complexes are located near the pyridine rings and π,π-stacking interactions between pyridine rings, nitrate ions and nitrile groups have been found.     

Molecular Dynamics Simulations of Peptides from the Central Domain of Smooth Muscle Caldesmon

Abstract

The central domain of smooth muscle caldesmon contains a highly charged region consisting of ten 13-residue repeats. Experimental evidence obtained from the intact protein and fragments thereof suggests that this entire region forms a single stretch of stable α-helix. We have carried out molecular dynamics simulations on peptides consisting of one, two and three repeats to examine the mechanism of α-helical stability of the central domain at the atomic level. All three peptides show high helical stability on the timescale of the MD simulations. Deviations from α-helical structure in all the simulations arise mainly from the formation of long stretches of π-helix. Interconversion between α-helical and π-helical conformations occurs through insertion of water molecules into α-helical hydrogen bonds and subsequent formation of reverse turns. The α-helical structure is stabilized by electrostatic interactions (salt bridges) between oppositely charged sidechains with i,i+4 spacings, while the π-helix is stabilized by i,i+5 salt bridge interactions. Possible i,i+3 salt bridges are of minor importance. There is a strong preference for salt bridges with a Glu residue N-terminal to a basic sidechain as compared to the opposite orientation. In the double and triple repeat peptides, strong i,i+4 salt bridges exist between the last Glu residue of one repeat and the first Lys residue of the next. This demonstrates a relationship between the repetitive nature of the central domain sequence and its ability to form very long stretches of α-helical structure.     

Osmotic parameters of red blood cells from umbilical cord blood

The transfusion of red blood cells from umbilical cord blood (cord RBCs) is gathering significant interest for the treatment of fetal and neonatal anemia, due to its high content of fetal hemoglobin as well as numerous other potential benefits to fetuses and neonates. However, in order to establish a stable supply of cord RBCs for clinical use, a cryopreservation method must be developed. This, in turn, requires knowledge of the osmotic parameters of cord RBCs. Thus, the objective of this study was to characterize the osmotic parameters of cord RBCs: osmotically inactive fraction (b), hydraulic conductivity (L_p), permeability to cryoprotectant glycerol (P_glycerol), and corresponding Arrhenius activation energies (E_a). For L_p and P_glycerol determination, RBCs were analyzed using a stopped-flow system to monitor osmotically-induced RBC volume changes via intrinsic RBC hemoglobin fluorescence. L_p and P_glycerol were characterized at 4 °C, 20 °C, and 35 °C using Jacobs and Stewart equations with the E_a calculated from the Arrhenius plot. Results indicate that cord RBCs have a larger osmotically inactive fraction compared to adult RBCs. Hydraulic conductivity and osmotic permeability to glycerol of cord RBCs differed compared to those of adult RBCs with the differences dependent on experimental conditions, such as temperature and osmolality. Compared to adult RBCs, cord RBCs had a higher E_a for L_p and a lower E_a for P_glycerol. This information regarding osmotic parameters will be used in future work to develop a protocol for cryopreserving cord RBCs.     

Synthesis of a 3'-naphthamido-LacNAc fluorescein conjugate with high selectivity and affinity for galectin-3

Described is the synthesis of a fluorescent LacNAc derivative appended with a 3'-deoxy-3'-naphthamido functionality, 2-(fluorescein-5/6-amido)ethyl 3-deoxy-3-(2-naphthamido)-beta-D-galactopyranosyl-(1-->4)-2-acetamido-2-deoxy-beta-D-glucopyranoside, which confers high affinity (Kd 170 nM) and selectivity for galectin-3 via a stacking interaction with Arg144. Its use as a selective and sensitive galectin-3 probe is demonstrated with fluorescence polarization measurements.     

Molecular insights into the genetic and haplotype diversity among four populations of Catla catla from Madhya Pradesh revealed through mtDNA cyto b gene sequences

In the present investigation, the genetic structure of four populations of Catla catla, sequences of mitochondrial gene, cytochrome b (cyto b) from four populations were sequenced and analyzed. The sequences of mitochondrial regions revealed high haplotype diversity and low nucleotide diversity. The lowest 249 polymorphic sites and 0.00 parsimony informative sites were detected in populations of Fish Federation Pond (CCFFB) whereas highest 330 polymorphic sites and 56 parsimony informative sites were detected in populations of Narmada River (CCNRH) in the cyto b gene sequences in Catla catla populations. The twelve different haplotypes were detected among the four populations studied, lowest population specific haplotype as 2.00 was observed in Fish Federation Pond (CCFFB) and highest was in Population of Narmada River and Tighra reservoir. Sequencing of cyto b gene revealed 12 number of haplotypes (h) with haplotype (gene) diversity (Hd) 0.8736 and nucleotide diversity (π) 0.6474. These data clearly indicated that, feral/wild population showing highest values of polymorphisms, parsimony, haplotype diversity showing good, healthy habitat is lotic water (Narmada River) and lentic water body (Tighra reservoir). The results also concluded that the partial cyto b is polymorphic and can be a potential marker to determine ecological habitat based genetic differentiation among the populations.     

First theoretical framework of di-substituted donor moieties of triphenylamine and carbazole for NLO properties: quantum paradigms of interactive molecular computation

The dependence of polarisability (α) and hyperpolarisability (β) on donor strength has been systematically studied by employing density functional theory method on triphenylamine (TPA) and carbazole (CZ) based compounds. The electronic structures, absorption spectra and non-linear optical (NLO) response were calculated by using quantum chemical methods. All the calculations were performed in gas phase in presence of solvent. The results reveal that the polarizability (α) and hyperpolarizability (β) significantly increased by the addition of second donor moiety. Similarly, the oscillator strength and light harvesting efficiency were also increased, while absorption wavelength was red-shifted by the addition of second donor moiety. These results indicate that the di-substituted donor is an effective way to improve NLO response. The TPA dyes possess a large second-order non-linear response and this is primarily because of the strong donor-π-acceptor conjugation that is ascribed to the excited state intramolecular charge transfer. These theoretical frameworks of carbon architecture might be advantageous to design other organic charge-transfer compounds.     

Correlations between functional porphyrin positions and accumulation in cancer cells

Porphyrin is accumulated in tumours due to its interaction with protein. Cancer therapy with porphyrin as a carrier molecule is attracting attention. Porphyrin displays two functional sites termed β- and meso-positions. A correlation between the functional position on the porphyrin molecule and the ability to accumulate in cancer cells is observed in the present study. The accumulation of porphyrin derivatives was determined by measuring fluorescence intensity after incubation for 2 and 24 h. The accumulation of cancer cells depended on the position and length of functional groups. Estimated binding constants between porphyrin and bovine serum albumin suggest that the position of functional groups leads to changes in binding affinity and influences the accumulation of porphyrin derivatives in cancer cells.