Membrane Active Arginine and Tryptophan Rich Peptides

Doctoral thesis, 2013

Genetic diseases, cancer and antibiotic resistant bacterial infections are causing many people a great deal of suffering every year. Treatment and cure of these medical conditions are desirable, but also challenging for the medical industry. Membrane-active peptides (MAPs) are a group of peptides that are very promising for all these medical applications. These peptides include the cell-penetrating peptides (CPPs) which have the ability to efficiently transport DNA, proteins and other macromolecules into cells, and the antimicrobial peptides (AMPs) that can kill or inhibit the growth of bacteria, fungi and parasites. The properties of these peptides are overlapping, and have been suggested to depend on both the peptide sequence and membrane constituents. The mechanisms of action of these peptides are, however, not yet fully understood. The goal with the work presented in this thesis, therefore is to better understand the mechanistic details of how membrane-active peptides bind to and interact with cellular membranes. The work focuses on the influence of the amino acids arginine and tryptophan on peptide function and membrane interaction, which has been investigated using cellular and physicochemical studies. The results from the work in this thesis indicate that the number and position of the amino acid tryptophan in the peptide sequence affect both cellular uptake and antibacterial properties. The biological effect seems partly related to the secondary structure of the peptides and the composition of the lipid membrane. The results also show that cellular uptake gains from increasing arginine content, and that proteoglycans at the cell surface specifically affect the cellular uptake of arginine-rich peptides. In addition, it is shown that the properties of the peptides may be affected by fluorescent labeling, and that this effect depends on the peptide amino acid sequence. In summary, these results give further information about how specific amino acids may affect the properties of the peptide, and how this regulates both membrane function and membrane specificity of membrane-active peptides.