Structure and Dynamics of Membrane Associated Peptides

Abstract: The peptide-membrane interaction is a key element for many biological functions, from cell signaling to cell internalization. In this thesis the peptide-membrane interaction of six different peptides have been studied with respect to their structure, membrane location and dynamics with spectroscopic methods. Penetratin and the N-terminal sequence of the bovine prion protein (1-30), bPrPp, belong to a class of peptides called cell-penetrating peptides (CPPs). CPPs are short, often highly basic peptides that have the ability to facilitate translocation of an attached hydrophilic cargo over cell-membrane. CD and NMR spectroscopy reveled that penetratin, the (supposedly) non-penetrating mutant pentratin(W48F,W56F) and bPrPp are all highly helical in membrane mimicking media. The position with respect to the bilayer is, however, very different for the three peptides, Penetratin is residing on the membrane surface with a slight tilt while bPrPp is transmembrane and penetratin(W48F,W56F) is somewere in between. These differences can explain the different impact these peptides have on membranesWe have also shown that penetratin can escape from vesicles when an electrochemical or pH gradient is present over the membrane, which support endocytotic internalization.Melittin is a 26 amino acid long residue long peptide and is the major component of the European honey bee venom. Many studies have shown that melittin induces a transient pore that causes leakage in both natural and artificial membranes. In paper IV we used melittin as a model-peptide to investigate how peptides affect lipid dynamics in model-membranes. We showed that carbon-13 relaxation of the lipids could be used to characterize peptide induced changes in lipid dynamicsThe voltage sensor is a domain of the voltage-dependent potassium channel containing several positively charged amino acids (usually arginines). The sensor undergoes a conformational change as a response to a membrane potential. Here, we have studied the membrane location of two fragments corresponding to the “paddle” domain of two different potassium channels, KvAP and HsapBK. NMR and fluorescence studies indicate that both peptides reside inside of the hydrophobic interior of the bilayer, which show that the fragment behave the same way as it does in the intact protein.All six of these peptides interact strongly with model-membranes and adopt a helical conformation even though they have very different biological function. The difference in biological function can instead be explained by the variation in membrane position and membrane dynamics of these peptides