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Endotoxin Effects on Synthesis of Phosphatidic Acid and Phosphatidic Acid–Derived Diacylglyceride Species
Published in Helmut Brade, Steven M. Opal, Stefanie N. Vogel, David C. Morrison, Endotoxin in Health and Disease, 2020
At the next level of specificity of protein-lipid interaction, a distinct binding site for PA has been identified on the raf kinase, which itself interacts with the small Gp ras in activation of the MAP kinase pathway (30). Previous data had implicated PA and/or DG both upstream and downstream of the small Gp ras in the MAP kinase signaling pathway (31,32). Taken together, these data imply that a number of specific intracellular signaling pathways involved in mitogenesis and inflammation have specific checkpoints such as PLCγ and raf (and, more questionably, ras itself), where PA may be necessary when membrane association is required of a signaling protein. This suggests that observations implicating PA as a necessary but not sufficient factor in both mitogenesis and inflammation may be correct (1,2,33–35).
Structure and Function of Cell Membranes, and Cellular Transport of Drugs
Published in Lelio G. Colombetti, Principles of Radiopharmacology, 1979
The concept of the plasma membrane can be traced back to 1855 when Nageli and Cramer7 observed that the surface of plant cells was unpermeable to “pigments in cherry juice” (as a sideline comment, it is of interest to note that the latter phenomenon is still being used as the “dye exclusion test” to assess the permeability of isolatedcells). A structural concept of this “cell-enclosing” layer was introduced in 1925, after the findings of Gorter and Grendei,8 who correlated the surface of erythrocytes with the area of a monomolecular film, obtained by spreading the extracted total cellular lipid. These results suggested a cell membrane consisting of two layers of lipid molecules standing on end and back to back, with hydrophilic ends (Figure 1) facing the aqueous intra- and extracellular environments (Figure 2). This phospholipid model of biological membranes consequently received strong support from studies using electron microscopy, showing a trilaminar appearance of cell membranes (Figure 3). However, the lipid bilayer concept was in disagreement with the experimentally determined surface tension for cells. The latter values were much lower than those obtained for a lipid-water interface. It was reported that the addition of cellular protein extracts lowered the surface tension between lipid and aqueous phase, making it more comparable to that of cells.9 These findings, together with observed physicochemical properties of cell membranes, suggested a role of proteins in membrane architecture and lead in 1935 to the postulation of a structural model by Danielli (Figure 4). The latter concept was subsequently revised and emerged in 1952 as the Davson-Danielli model of biological membranes.10 The various modifications of the initially introduced model, particularly aspects suggested by Robertson11 (Figure 5), focused on the role of proteins and on the nature of protein-lipid interaction. The final Davson-Danielli-Robertson model (also known as “unit membrane” model) depicts in the center of the membrane two lipid layers consisting of fatty acid residues facing each other and, on both surfaces of the membrane, nonpolar layers of bound protein. The latter, in some places, penetrates the entire bilayer, resulting in membrane “pores” (Figure 6). The model also postulates the existence on both surfaces of loosely attached adsorbed protein. Polar interaction between protein molecules was suggested to explain cell membrane integrity, despite the existence of the pores.
Interaction of S-layer proteins of Lactobacillus kefir with model membranes and cells
Published in Journal of Liposome Research, 2018
Axel Hollmann, Lucrecia Delfederico, Nuno C. Santos, E. Anibal Disalvo, Liliana Semorile
The aim of the present work was to gain an understanding of structural and chemical properties of L. kefir S-layer proteins, and study in depth the interaction of S-layer proteins with lipid membranes. In this context, the use of lipid monolayer to follow the kinetic of protein insertion in the monolayers revealed to be a useful tool specially to track the protein–lipid interaction in a dynamic perspective (Disalvo et al., 2013a; Hollmann et al., 2010b, 2016).