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The aim of this study is to investigate the interactions between TAT peptides and a neutral DOPC bilayer by using neutron lamellar diffraction. The distribution of TAT peptides and the perturbation of water distribution across the DOPC bilayer were revealed. When compared to our previous study on an anionic DOPC/DOPS bilayer (X. Chen et al., Biochim Biophys Acta. 2013. 1828 (8), 1982–1988), a much deeper insertion of TAT peptides was found in the hydrophobic core of DOPC bilayer at a depth of 6.0 Å from the center of the bilayer, a position close to the double bond of fatty acyl chain. We conclude that the electrostatic attractions between the positively charged TAT peptides and the negatively charged headgroups of phospholipid are not essential for the direct translocation. Furthermore, the interactions of TAT peptides with the DOPC bilayer were found to vary in a concentration-dependent manner. A limited number of peptides first associate with the phosphate moieties on the lipid headgroups by using the guanidinium ions pairing. Then the energetically favorable water defect structures are adopted to maintain the arginine residues hydrated by drawing water molecules and lipid headgroups into the bilayer core. Such bilayer deformations consequently lead to the deep intercalation of TAT peptides into the bilayer core. Once a threshold concentration of TAT peptide in the bilayer is reached, a significant rearrangement of bilayer will happen and steady-state water pores will form. [ABSTRACT FROM AUTHOR]

The objectives of this study were to identify the chemical composition, monosaccharide composition, and molecular weight (Mw) of the polysaccharide (LBP) extract from Lycium barbarum L., and investigate the effects of Ca2+ on the zeta potential, rheological properties, infrared spectra (IR), and structure as well as the gelation mechanism of the LBP. The results showed that the LBP was an acidic glycoprotein mixture with an Mw of 4.05 × 105 Da. The addition of Ca2+ first decreased and then increased the absolute value of zeta potential. The elastic modulus (G'), complex viscosity (η*), and stress relaxation modulus (G(t)) of LBP increased with an increase of Ca2+ concentration, and reached the maximum value at the concentration of 12 mM. IR showed that the typical peak wavenumber of the LBP has changed in the presence of Ca2+. SEM and AFM analysis confirmed that Ca2+ could improve the formation of gel network structure in LBP. In addition, the electrostatic interaction and the calcium bridges produced by the addition of Ca2+ played a key role in the formation of the gel network structure. These findings will benefit the application of LBP in the food and pharmaceutical industries. [Display omitted] • Effect of Ca2+ on the rheological properties and structure of LBP was investigated. • Gelation mechanism of LBP was also elucidated. • Increasing concentration of Ca2+ improved rheological properties of the LBP gels. • Ca2+ increased the stability of LBP gel network structure. • Electrostatic interaction was crucial to LBP gel network structure formation. [ABSTRACT FROM AUTHOR]