Secondary structure and position of the cell-penetrating peptide transportan in SDS micelles as determined by NMR

Transportan is a 27-residue peptide (GWTLN SAGYL LGKIN LKALA ALAKK IL-amide ) which has the ability to penetrate into living cells carrying a hydrophil ic load. Transportan is a chimeric peptide constructed from the 12 N-termin al residues of galanin in the N-terminus with the lit-residue sequence of m astoparan in the C-terminus and a connecting lysine. Circular dichroism stu dies of transportan and mastoparan show that both peptides have close to ra ndom coil secondary structure in water. Sodium dodecyl sulfate (SDS) micell es induce 60% helix in transportan and 75% helix in mastoparan. The 600 MHz H-1 NMR studies of secondary structure in SDS micelles confirm the helix i n mastoparan and show that in transportan the helix is localized to the mas toparan part, The less structured N-terminus of transportan has a secondary structure similar to that of the same sequence in galanin [Ohman, A., et a l. (1998) Biochemistry 37, 9169-9178]. The position of mastoparan and trans portan relative to the SDS micelle surface was studied by adding spin-label ed 5-doxyl- or 12-doxyl-stearic acid or Mn2+ to the peptide/ micelle system . The combined results show that the peptides are for the most part buried in the SDS micelles, Only the C-terminal parts of both peptides and the cen tral segment connecting the two parts of transportan are clearly surface ex posed, For mastoparan. the secondary chemical shifts of the amide protons w ere found to vary periodically and display a pattern almost identical to th ose reported for mastoparan in phospholipid bicelles [Vold, R,, et al. (199 7) J. Biomol. NMR 9, 329-335]. indicating similar structures and interactio ns in the two membrane-mimicking environments.