NMR solution structure and membrane interaction of the N-terminal sequence (1-30) of the bovine prion protein.

The structure and membrane interaction of the N-terminal sequence (1-30) of the bovine prion protein (bPrPp) has been investigated by NMR spectroscopy in phospholipid membrane mimetic systems. CD spectroscopy revealed that the peptide adopts a largely alpha-helical structure in zwitterionic bicelles as well as in DHPC micelles but has a less degree of alpha-helix structure in partly charged bicelles. The solution structure of bPrPp was determined in DHPC micelles, and an alpha-helix was found between residues Ser8 and Ile21. The residues within the helical region show slow amide hydrogen exchange. Translational diffusion measurements in zwitterionic q = 0.5 bicelles show that the peptide does not induce aggregation of the bicelles. Increased quadrupolar splittings were observed in the outer part of the (2)H spectrum of DMPC in q = 3.5 bicelles, indicating that the peptide induces a certain degree of order in the bilayer. The amide hydrogen exchange and the (2)H NMR results are consistent with a slight positive hydrophobic mismatch and that bPrPp forms a stable helix that inserts in a transmembrane location in the bilayer. The structure of bPrPp and its position in the membrane may be relevant for the understanding of how the N-terminal (1-30) part of the bovine PrP functions as a cell-penetrating peptide. These findings may lead to a better understanding of how the prion protein accumulates at the membrane surface and also how the conversion into the scrapie form is carried out.