Surfactin-triggered small vesicle formation of negatively charged membranes: a novel membrane-lysis mechanism

The molecular mode of action of the lipopeptide SF with zwitterionic and negatively charged model membranes has been investigated with solid-state NMR, light scattering, and electron microscopy. It has been found that this acidic lipopeptide (negatively charged) induces a strong destabilization of negatively charged micrometer-scale liposomes, leading to the formation of small unilamellar vesicles of a few 10s of nanometers. This transformation is detected for very low doses of SF (Ri = 200) and is complete for Ri = 50. The phenomenon has been observed for several membrane mixtures containing phosphatidylglycerol or phosphatidylserine. The vesicularization is not observed when the lipid negative charges are neutralized and a cholesterol-like effect is then evidenced, i.e., increase of gel membrane dynamics and decrease of fluid membrane microfluidity. The mechanism for small vesicle formation thus appears to be linked to severe changes in membrane curvature and could be described by a two-step action: 1), peptide insertion into membranes because of favorable van der Waals forces between the rather rigid cyclic and lipophilic part of SF and lipid chains and 2), electrostatic repulsion between like charges borne by lipid headgroups and the negatively charged SF amino acids. This might provide the basis for a novel mode of action of negatively charged lipopeptides.     

Relationship between the intra-erythrocyte sodium composition and the membrane lipoprotein composition among different mammal species

Internal sodium and lipoprotein composition of RBCs of nine mammalian species are measured. A significant correlation can be demonstrated between the erythrocyte mean sodium value of studied species and the membrane protein/lipid ratio (r = 0.80, alpha less than 0.01). Erythrocyte internal sodium can be correlated with membrane-free cholesterol but not with the phospholipid fractions.     

Cu(II)—(lAsp)n system. Spectroscopic evidence of hexatomic chelate ring formation

The study of the Cu(II)-(L Asp)_n system using circular dichroism and potentiometric data has provided evidence indicating the formation of two complexes in a two step process. In the first (I) of these complexes, obtained at pH 4.5, two carboxyl residues are bound to the metal. This complex partially inhibits the transition from α helix to nonperiodic conformation. In the second complex (II) two peptide nitrogens and two carboxylate oxygens are bound to each Cu(II) ion forming two hexatomic chelate rings. The CD spectral pattern is then the opposite of what is obtained when a five-membered chelate ring is formed.     

Isolation and characterization of an expressed hypervariable gene coding for a breast-cancer-associated antigen.

A human gene and cDNA coding for a breast-cancer-associated antigen (H23Ag) were isolated and characterized. The gene contains two exons and one intron. Part of the second exon is a tandem repeat array (TRA) consisting of multiple 60-bp G + C-rich units. We report here the characterization of unique sequences that are found in the H23Ag gene and cDNA, in addition to the 60-bp repeats. Analysis of the cDNA sequences revealed a putative ATG start codon preceded by two overlapping initiation consensus sequences (CCACC). The open reading frame determines an amino acid (aa) sequence consisting of three regions. The first region contains an initiating methionine and a highly hydrophobic putative signal peptide. This is followed by a variable number of highly conserved 20-aa repeat units (TRA). The last region, C-terminal to TRA, contains four potential N-linked glycosylation sites. The genomic nucleotide sequences demonstrate a putative promoter region that includes a 'TATA' box. A putative estrogen regulatory element is located 5' to the promoter region. The characterization of the gene and cDNA coding for the H23Ag presented here, may help to elucidate its possible function in human breast cancer.