Quantitative use of paramagnetic relaxation enhancements for determining orientations and insertion depths of peptides in micelles.

We describe the background and implementation of a method to determine, at atomic resolution, the insertion depths and orientations of peptides embedded in micelles. A nonperturbing paramagnetic agent--Gd(DTPA-BMA)--was used to induce paramagnetic relaxation enhancements (PREs) of peptide atoms inside the micelle. By calibrating these PREs it was possible to translate them into distance restraints that could be used for structure calculation. We demonstrate this here on the antimicrobial peptides novicidin and novispirin. Characterization of the interactions between antimicrobial peptides and membranes is important for understanding of their biological activities and functions, and a further development of tools to study these interactions is described.