The utility of conventional peptides in pharmaceutical and biotechnological applications is limited by their poor stability and bioavailability. Cyclotides are plant derived mini-proteins with unique structural properties that make them exceptionally stable and have a range of exciting applications in drug design and agriculture. Beside the variety of intrinsic activities, there are still many unanswered questions regarding the mechanism involved in cyclotides activity. Understanding how they exert their biological effects is a crucial step and is the basis of this proposal. Recent evidence has emerged that these actions are mediated by membrane interactions and this study will determine the chemical and biophysical basis for these interactions. The main goal of this project is to explore the interaction of a selected set of cyclotides with biological membranes. The specific objectives are to evaluate: 1) the structural features important for the membrane binding of cyclotides; 2) the structural basis of membrane selectivity; 3) if the self-association properties of cyclotides are involved in their mechanism of action; 4) the biophysical basis for the effects of cyclotides on living cells; 5) the information from objective 1-4, together with bioactivity data to rationalise the bioactivity of cyclotides. Understanding how cyclotides exert their biological activities will provide valuable information that can be applied in subsequent drug design studies. The outgoing host lab has a strong background on cylotides and several facilities that can be optimized for peptide-lipid studies (NMR and fluorescence spectroscopies, isothermal titration calorimetry and surface Plasmon resonance). An advanced training to complement applicant specific expertise and skills in peptide-lipid interaction, obtained previously in return host lab, will be acquired. This knowledge exchange between outgoing and return host organization will create an environment for future collaborations.