Amyloids are proteinaceous aggregates related to the so-called conformational diseases, such as Alzheimer's and prion diseases. The cytotoxicity of amyloids may be related to the interaction of the amiloidogenic peptides or proteins with the cell membrane. In order to gain information on the physico-chemical effects of amyloids on membranes, we have studied the interaction of the human prion amyloidogenic fragment PrP 185-206 with negatively charged model membranes. The results show that the peptide causes the destabilization of the membrane, making it permeable to potassium ions and to charged organic compounds. This effect correlates with the interaction of the peptide with the membrane, causing a variation in the magnitude of the electrostatic surface and dipole membrane potentials. This effect on the electrostatic properties of the membranes may help explaining the observed permeability: a neutralization of the surface negative charge and a decrease of the inside-positive dipole potential would facilitate the translocation of positive ions. The structural analysis of the peptide in the presence of model membranes reveals that it adopts a predominantly unordered structure without any signs of amyloid formation. The results may be relevant in relation to the recently described cell toxic capacity of the peptide.

Three pure lipid-transport proteins (LTPs) were isolated from Nigella sativa seeds. The effects of the three LTPs on release of ANTS probe from the inner volume were studied using fluorescence in liposomes of different lipid composition. It was shown that all LTPs had a dose-dependent effect on the liposome permeability.Non-specific lipid-transport proteins (LTPs) belong to a family of proteins that are widely distributed in plants [1,2]. They were isolated from seeds of various classes of plants such as maize [3], wheat [4], barley [5], and rice [6] in addition to leaves of several plants [7]. A comparison of the physicochemical properties of the isolated compounds reveals common trends in the molecular structure. They are a homogeneous family of basic peptides 90-93 amino acids long with eight cysteine units in conserved positions that form a hydrophobic cavity [8]. LTPs are typically capable in vitro of transferring glycerophospholipids or galactolipids through membranes [1, 8]. They can inhibit in vivo the growth of bacteria and fungi [8]. One of the proposed mechanisms of the antifungal activity of several LTPs (Ha-AP10 from Helianthus annuus [9], LTP2 from wheat [10], and LTP from onion [11]) is the induction by them of increased permeability of pathogen plasmatic membranes for small organic molecules and inorganic ions.It would be useful to find trends in their effects on the structural properties of lipid membranes in order to understand better differences in the effectiveness with which LTP from various sources interact with lipids.Our goal was to study the effects of three LTP isolated from Nigella sativa seeds (Ns-LTPs) that had different physicochemical properties (LTP1, LTP2, LTP3) on the permeability of model lipid membranes.We have previously isolated and studied the physicochemical properties of Ns-LTP1 from N. sativa seeds [12]. Here we continued the detailed investigation of the peptide composition from N. sativa seeds and found two more peptides that belonged to the same class as LTP1 but had different molecular weights (MWs).Chromatography of total peptides from N. sativa seeds over affinity sorbent Hi Trap Heparin HP produced four basic fractions that were eluted by different NaCl concentrations (0 M, 0.1, 0.5, and 1). According to mass spectrometry, a component with MW 8130 Da dominated the fraction eluted by buffer A. Then, the component was purified by RP-HPLC, which produced four fractions. Mass spectral analysis of these showed that fraction 4 was homogeneous and contained a polypeptide of MW 8130 Da (LTP2).The 0.1-M fraction contained several protein components with MW in the range 9-12 kDa. The dominant polypeptide had MW 9602 Da. The polypeptide was purified by RP-HPLC, which produced eight fractions. Mass spectral analysis of these showed that fraction 4 was homogeneous and contained a component with MW 9602 Da, which we called Ns-LTP1. We sequenced its N-terminus and determined the amino-acid composition and number of cysteines in order to confirm that it was an LTP [12].