A great deal of data has been amassed suggesting that cationic peptides are able to translocate into eucaryotic cells in a temperature-independent manner. Although such peptides are widely used to promote the intracellular delivery of bioactive molecules, the mechanism by which this cell-penetrating activity occurs still remains unclear. Here, we present an in vitro study of the cellular uptake of peptides, originally deriving from protegrin (the SynB peptide vectors), that have also been shown to enhance the transport of drugs across the blood-brain barrier. In parallel, we have examined the internalization process of two lipid-interacting peptides, SynB5 and pAntp-(43-58), the latter corresponding to the translocating segment of the Antennapedia homeodomain. We report a quantitative study of the time-and dose-dependence of internalization and demonstrate that these peptides accumulate inside vesicular structures. Furthermore, we have examined the role of endocytotic pathways in this process using a variety of metabolic and endocytosis inhibitors. We show that the internalization of these peptides is a temperatureand energy-dependent process and that endosomal transport is a key component of the mechanism. Altogether, our results suggest that SynB and pAntp-(43-58) peptides penetrate into cells by an adsorptive-mediated endocytosis process rather than temperature-independent translocation.

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Receptors for the Fc region of IgG from neonatal rat intestinal brush borders were solubilized using 3-[(3-cholamidopropyl)dimethyl-ammonio]-1-propane sulfonate and purified by affinity chromatography. Analysis of IgG-binding material by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing conditions reveals two components with apparent Mr of 41 000-50 000 and 15 000. The larger component is glycosylated and may dimerize, giving a 100-110-kDa band on nonreduced gels. Both proteins are localized in the proximal small intestine, where IgG is specifically taken up during the first three weeks of neonatal life, and disappear when specific transport stops after weaning. Electron irradiation of brush borders shows that the functional unit for IgG binding has a molecular weight in situ of 110 kDa. These data suggest that a dimer of the 41-50-kDa protein together with the 15 kDa and other proteins may mediate intestinal transport of maternal IgG.

An improved antibody modelling algorithm has been developed which incorporates significant improvements to the earlier versions developed by Martin et al. (1989, 1991), Pedersen et al. (1992) and Rees et al. (1996) and known as AbM (Oxford Molecular). The new algorithm, WAM (for Web Antibody Modelling), has been launched as an online modelling service and is located at URL http://antibody.bath.ac.uk. Here we provide a summary only of the important features of WAM. Readers interested in further details are directed to the website, which gives extensive background information on the methods employed. A brief description of the rationale behind some of the newer methodology (specifically, the knowledge-based screens) is also given.

Several models for interactions between trifluoroethanol (TFE) and peptides and proteins have recently been proposed, but none have been able to rationalize the puzzling observations that on the one hand TFE can stabilize some hydrophobic interactions in secondary structures, but on the other can also melt the hydrophobic cores of globular proteins. The former is illustrated in this paper by the effect of TFE on a short elastin peptide, GVG(VPGVG)(3), which forms type II beta-turns stabilized by hydrophobic interactions between two intra-turn valine side chains. This folding, driven by increasing the entropy of bulk water, is stimulated in TFE-water mixtures and/or by raising the temperature. To explain these apparently contradictory observations, we propose a model in which TFE clusters locally assist the folding of secondary structures by first breaking down interfacial water molecules on the peptide and then providing a solvent matrix for further side chain--side chain interactions. This model also provides an explanation for TFE-induced transitions between secondary structures, in which the TFE clusters may redirect non-local to local interactions.