LOCATION OF M13 COAT PROTEIN IN SODIUM DODECYL-SULFATE MICELLES AS DETERMINED BY NMR

The major coat protein (gVIIIp) of bacteriophage M13 solubilized in so dium dodecyl sulfate (SDS) detergent micelles was used as a model syst em to study this protein in the lipid-bound form. In order to probe th e position of gVIIIp relative to the SDS micelles, stearate was added, spin-labeled at the 5- or 16-position with a doxyl group containing a stable nitroxide radical. The average position of the spin-labels in the micelles was derived from the line broadening of the resonances in the C-13 spectrum of SDS. Subsequently, we derived a model of the rel ative position of gVIIIp in the SDS micelle from the effect of the spi n-labels on the gVIIIp resonances, monitored via H-1-N-15 HSQC and TOC SY experiments. The results are consistent with the structure of gVIII p having two helical strands. One strand is a long hydrophobic helix t hat spans the micelle, and the other is a shorter amphipathic helix on the surface of the micelle. These results are in good agreement with the structure of gVIIIp in membranes proposed by McDonnell et al. on t he basis of solid state NMR data [McDonnell, P. A., Shon, K., Kim, Y., & Opella, S. J. (1993) J. Mol.Biol. 233, 447-463]. This study indicat es that high-resolution NMR on this membrane protein, solubilized in d etergent micelles, is a very suitable technique for mimicking these pr oteins in their natural environment. Furthermore, the data indicate th at the structure of the micelle near the C-terminus of the major coat protein is distorted. This is probably due to the interaction of the p ositively charged lysine side chains with the sulfate head groups of t he detergent molecules.