7 research outputs found
Resummation of divergent pertubation series. Application to calculations of vibrational energy spectrum of different molecules
Influence of peat formation conditions on the transformation of peat deposit organic matter
Heat conductivity of aerogel-based rolled materials for high-thermal isolation for equipment and pipelines
Concentrations and Composition of Sphagnum Peat Lipids Depending on Temperature in the Climatic Zones of Western Siberia
Lipid-binding properties of synthetic peptide fragments of human apolipoprotein A-II.
Human apolipoprotein A-II (apo A-II) consists of three potential amphipathic helices of 17 residues each, which contribute to the lipid-binding properties of this apolipoprotein. The conformation and lipid-binding properties of these peptides, either as single-helix or as two-helix peptides, were investigated by turbidity, fluorescence, electron-microscopy and circular-dichroism measurements, and are compared in this article. The lipid affinity of shorter C-terminal segments of apo A-II was compared with those of the single-helix or two-helix peptides, to define the minimal peptide length required for stable complex formation. The properties of the apo-A-II-(13-48)-peptide were further compared with those of the same segment after deletion of the Ser31 and Pro32 residues, because the deleted apo-A-II-(13-30)-(33-48)-peptide, is predicted to form a long uninterrupted helix. The single helices of apo A-II could not form stable complexes with phospholipids, and the helix-turn-helix segment spanning residues 13-48 was not active either. The apo-A-II-(37-77)-peptide and the apo-A-II-(40-73)-peptide could form complexes with lipids, which appear as discoidal particles by negative-staining electron microscopy. The shortest C-terminal domain of apo A-II able to associate with lipids to form stable complexes was the apo-A-II-(40-73)-peptide, which consisted of the C-terminal helix, a beta-turn and part of the preceding helix. The shorter apo-A-II-(49-77)-peptide, and the helical apo-A-II-(13-30)-(33-48)-peptide, could also associate with phospholipids. The complexes formed were, however, less stable, as they dissociated outside the transition temperature range of the phospholipid. These data suggest that the C-terminal pair of helices of apo A-II, which is the most hydrophobic pair, is responsible for the lipid-binding properties of the entire protein. The N-terminal pair of helices of apo A-II at residues 13-48 does not associate tightly with lipids. The degree of internal similarity and the cooperativity between the helical segments of apo A-II is thus less pronounced than in apo A-I or apo A-IV. The N-terminal and C-terminal domains of apo A-II appear to behave as two distinct entities with regard to lipid-protein association