Receptor Arrangement In Myoblasts And Model Membranes

Glycosphingolipids are the carbohydrate-bearing lipids of animal cell surfaces. They are being investigated for their structural effects, for their role as recognition sites for hormones, toxins, viruses, and for their involvement in cell-cell interactions. Their physical behaviour in membranes--i.e., their exposure, distribution, peculiar acyl chain characteristics, sugar headgroup arrangement, and interactions--have become questions of considerable debate since these are the very factors thought to regulate their roles as structural components and attachment/recognition sites.;A major interest for us has been to apply freeze-etch electron microscopy to receptor studies in membranes. We developed its use for glycoproteins in cultured cell membranes and attempted to extend this work to glycolipids. The Pfenninger device, originally designed to allow freeze-fracture electron microscopy of cells grown in culture, was used in a novel way to visualize the surface distribution of wheat germ agglutinin and concanavaline A receptors. Since glycoproteins rather than glycolipids are predominately labelled using lectins, the use of monoclonal antibodies to glycolipids was explored. Model membrane systems were used in an attempt to quantitate the data available from freeze-etch electron microscopy using native lectins to mark glycosphingolipid distribution. Limitations to the freeze-etch technique for glycosphingolipid localization were demonstrated, which would restrict its application to glycosphingolipid distribution in intact cells.;Recent work (reviewed by Curatolo in Biochim. Biophys. Acta 906, 111-136 (1987)) has emphasized the need to evolve beyond studies of membranes that are highly cooperative in their phase behavior in order to understand cell membranes. We have developed fatty acid spin-labelled glycolipids that can potentially be used equally well in any membrane. We synthesized a novel long chain (24-carbon) fatty acid spin label and used this new probe to address the fate of long fatty acid chains of glycosphingolipids in membranes of non-interdigitating phosphatidylcholines. Finally we have critically addressed the question of lateral distribution, accessibility to macromolecules and freeze-etch electron microscopy of the neutral glycosphingolipid, globoside, in cooperative and non-cooperative bilayer membranes, and the effect of glycolipid fatty acid chain length upon these factors

Antibodies inhibit prion propagation and clear cell cultures of prion infectivity

Prions are the transmissible pathogenic agents responsible for diseases such as scrapie and bovine spongiform encephalopathy. In the favoured model of prion replication, direct interaction between the pathogenic prion protein (PrPSc) template and endogenous cellular prion protein (PrPC) is proposed to drive the formation of nascent infectious prions. Reagents specifically binding either prion-protein conformer may interrupt prion production by inhibiting this interaction. We examined the ability of several recombinant antibody antigen-binding fragments (Fabs) to inhibit prion propagation in cultured mouse neuroblastoma cells (ScN2a) infected with PrPSc. Here we show that antibodies binding cell-surface PrPC inhibit PrPSc formation in a dose-dependent manner. In cells treated with the most potent antibody, Fab D18, prion replication is abolished and pre-existing PrPSc is rapidly cleared, suggesting that this antibody may cure established infection. The potent activity of Fab D18 is associated with its ability to better recognize the total population of PrPC molecules on the cell surface, and with the location of its epitope on PrPC. Our observations support the use of antibodies in the prevention and treatment of prion diseases and identify a region of PrPC for drug targeting