Kenichi Aburai

Altered sphingoid base profiles predict compromised membrane structure and permeability in atopic dermatitis

BACKGROUND Ceramide hydrolysis by ceramidase in the stratum corneum (SC) yields both sphingoid bases and free fatty acids (FFA). While FFA are key constituents of the lamellar bilayers that mediate the epidermal permeability barrier, whether sphingoid bases influence permeability barrier homeostasis remains unknown. Pertinently, alterations of lipid profile, including ceramide and ceramidase activities occur in atopic dermatitis (AD). OBJECT We investigated alterations in sphingoid base levels and/or profiles (sphingosine to sphinganine ratio) in the SC of normal vs. AD mice, a model that faithfully replicates human AD, and then whether altered sphingoid base levels and/or profiles influence(s) membrane stability and/or structures. METHODS Unilamellar vesicles (LV), incorporating the three major SC lipids (ceramides/FFA/cholesterol) and different ratios of sphingosine/sphinganine, encapsulating carboxyfluorescein, were used as the model of SC lipids. Membrane stability was measured as release of carboxyfluorescein. Thermal analysis of LV was conducted by differential scanning calorimetry (DSC). RESULTS LV containing AD levels of sphingosine/sphinganine (AD-LV) displayed altered membrane permeability vs. normal-LV. DSC analyses revealed decreases in orthorhombic structures that form tightly packed lamellar structures in AD-LV. CONCLUSION Sphingoid base composition influences lamellar membrane architecture in SC, suggesting that altered sphingoid base profiles could contribute to the barrier abnormality in AD.

Synthesis and evaluation of a novel liposome containing BPA-peptide conjugate for BNCT.

We aimed at securing sufficient concentrations of (10)B in boron neutron capture therapy (BNCT) by developing a new drug delivery system. We have designed and developed a novel lipid analog and succeeded in using it to develop the new boron component liposome. It consisted of three different kinds of amino acid derivatives and two fatty acids, and could react directly with the peptide synthesized first on resin by Fmoc solid-phase synthesis. In this study, lipid analog conjugated with HIV-TAT peptide (domain of human immunodeficiency virus TAT protein) and boronophenylalanine (BPA) was synthesized and successfully incorporated into liposomes.

Surfactant-like properties of an amphiphilic α-helical peptide leading to lipid nanodisc formation.

Nanodiscs are self-assembled discoidal nanoparticles composed of amphiphilic α-helical scaffold proteins or peptides that wrap themselves around the circumference of a lipid bilayer in a beltlike manner. In this study, an amphiphilic helical peptide that mimics helix 10 of human apoA-I was newly synthesized by solid phase peptide synthesis using Fmoc chemistry, and its physicochemical properties, including surface tension, self-association, and solubilization abilities, were evaluated and related directly to nanodisc formation. The synthesized peptide having hydrophobic and hydrophilic faces behaves like a general surfactant, affording a critical association concentration (CAC) of 2.7 × 10(-5) M and a γCAC of 51.2 mN m(-1) in aqueous solution. Interestingly, only a peptide solution above its CAC was able to microsolubilize L-α-dimyristoylphosphatidylcholine (DMPC) vesicles, and lipid nanodiscs with an average diameter of 9.5 ± 2.7 nm were observed by dynamic light scattering and negative stain transmission electron microscopy. Moreover, the ζ potentials of the lipid nanodiscs were measured for the first time as a function of pH, and the values changed from positive (20 mV) to negative (-30 mV). In particular, nanodisc solutions at acidic pH 4 (20 mV) or basic pH 9 (-20 mV) were found to be stable for more than 6 months as a result of the electrostatic repulsion between the particles.

Promotion of crystalline cellulose degradation by expansins from Oryza sativa

Main conclusionEnzymatic activities ofOryza sativaexpansins, which were heterologously overexpressed inEscherichia coli, were analyzed. Results suggested that expansins promote degradation of cellulose by cellulase in a synergistic manner.AbstractSustainable production of future biofuels is dependent on efficient saccharification of lignocelluloses. Expansins have received a lot of attention as proteins promoting biological degradation of cellulose using cellulase. The expansins are a class of plant cell wall proteins that induce cell wall loosening without hydrolysis. In this study, the expansins from Oryza sativa were classified using phylogenetic analysis and five proteins were selected for functional evaluation. At low cellulose loading, the cellulase in expansin mixtures was up to 2.4 times more active than in mixtures containing only cellulase, but at high cellulose loading the activity of cellulase in expansin mixtures and cellulase only mixtures did not differ. Furthermore, expansin activity was greater in cellulase mixtures compared with cellulase-deficient mixtures. Therefore, the expansins showed significant synergistic activity with cellulase. Expansin may play an important role in efficient saccharification of cellulose.

Surface adsorption and vesicle formation of dilauroylphosphatidylcholine in room temperature ionic liquids

Surface chemical properties of a phospholipid, dilauroylphosphatidylcholine (DLPC), in two ionic liquids (ILs), 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF(4)) and hexafluorophosphate (bmimPF(6)), were investigated by means of surface tension, dynamic light-scattering, and freeze-fracture transmission electron microscopy. It was found that DLPC shows finite solubility in the ILs and spontaneously forms vesicles with size distribution around 400 nm in diameter above the critical vesicular concentration (CVC) of 0.040 wt.% (in bmimBF(4)) and approx. 0.08 wt.% (in bmimPF(6)). Other than the CVC value, anion specificity of the ILs was also seen in the temperature effect on the vesicular aggregation; that is, a temperature-induced reversible aggregation was observed in bmimPF(6), but not in bmimBF(4). The differences in the vesicular stability against the temperature-induced aggregation could be attributed to differences in the interaction between anion species of the ILs and zwitterionic phosphatidylcholine head groups. The apparent molecular area occupied by DLPC at the air/solution interface was estimated to be 0.37 nm(2) in bmimBF(4) and 0.20 nm(2) in bmimPF(6) by applying the Gibbs adsorption equation. These values are much smaller than the molecular area of 0.69 nm(2) reported for the hydrated DLPC bilayer of lamellar liquid-crystalline phase. This result is not consistent with the traditional Gibbs adsorption model, but can be interpreted in terms of a picture for the surface adsorption of soluble amphiphiles proposed by Moroi et al. Differential scanning calorimetric study is also reported regarding the phase transition behavior of DLPC bilayer solvated by the ILs.

Enhancement of Cellulose Degradation by Cattle Saliva

Saccharification of cellulose is a promising technique for producing alternative source of energy. However, the efficiency of conversion of cellulose into soluble sugar using any currently available methodology is too low for industrial application. Many additives, such as surfactants, have been shown to enhance the efficiency of cellulose-to-sugar conversion. In this study, we have examined first whether cattle saliva, as an additive, would enhance the cellulase-catalyzed hydrolysis of cellulose, and subsequently elucidated the mechanism by which cattle saliva enhanced this conversion. Although cattle saliva, by itself, did not degrade cellulose, it enhanced the cellulase-catalyzed degradation of cellulose. Thus, the amount of reducing sugar produced increased approximately 2.9-fold by the addition of cattle saliva. We also found that non-enzymatic proteins, which were present in cattle saliva, were responsible for causing the enhancement effect. Third, the mechanism of cattle saliva mediated enhancement of cellulase activity was probably similar to that of the canonical surfactants. Cattle saliva is available in large amounts easily and cheaply, and it can be used without further purification. Thus, cattle saliva could be a promising additive for efficient saccharification of cellulose on an industrial scale.