Dodecylphosphocholine micelles as a membrane like environment: new resultsfrom NMR relaxation and paramagnetic relaxation enhancement analysis

To further examine to what extent a dodecylphosphocholine (DPC) micelle mim ics a phospbatidylcholine bilayer environment, we performed C-13, H-2, and P-31 NMR relaxation measurements. Our data show that the dynamic behavior o f DPC phosphocholine groups at low temperature (12 degrees C) corresponds t o that of a phosphatidylcholine interface at high temperature (51 degrees C ). In the presence of helical peptides, a PMP1 fragment, or an annexin frag ment, the DPC local dynamics are not affected whereas the DPC aggregation n umber is increased to match an appropriate area/volume ratio for accommodat ing the bound peptides. We also show that quantitative measurements of para magnetic relaxation enhancements induced by small amounts of spin-labeled p hospholipids on peptide proton signals provide a meaningful insight on the location of both PMP1 and annexin fragments in DPC micelles. The paramagnet ic contributions to the relaxation were extracted from intra-residue cross- peaks of NOESY spectra for both peptides. The location of each peptide in t he micelles was found consistent with the corresponding relaxation data. As illustrated by the study of the PMP1 fragment, paramagnetic relaxation dat a also allow us to supply the missing medium-range NOEs and therefore to co mplete a standard conformational analysis of peptides in micelles.