2.B.10 The Synthetic CPP, Transportan (Transportan) Family
Transportan is a chimeric cell-penetrating peptide constructed from the peptides galanin (P47216) and mastoparan (TC#1.C.32). It has the ability to internalize living cells carrying a hydrophilic load. Bárány-Wallje et al. (2004) determined its NMR solution structure and investigated the position of transportan in neutral bicelles. The structure revealed a well-defined alpha-helix in the C-terminal mastoparan part of the peptide and a weaker tendency to form an alpha-helix in the N-terminal domain. The position of the peptide in relation to the membrane showed that the peptide lies parallel to, and in the head-group region of the membrane surface. These arginine-rich CPPs (SR9, HR9 and PR9) can form stable complexes with plasmid DNA at the optimized nitrogen/phosphate ratio of 3 and deliver plasmid DNA into Paramecium caudatum in a noncovalent manner (Dai et al., 2011).
The kinetics and thermodynamics of binding of transportan 10 (tp10) and four of its variants to phospholipid vesicles, and the kinetics of peptide-induced dye efflux, have been compared by Yandek et al. (2008). Tp10 is a 21-residue, amphipathic, cationic, cell-penetrating peptide similar to helical antimicrobial peptides. The tp10 variants examined include amidated and free peptides, and replacements of tyrosine by tryptophan. Carboxy-terminal amidation or substitution of tryptophan for tyrosine enhances binding and activity. The Gibbs energy for insertion into the bilayer core was calculated using hydrophobicity scales of residue transfer from water to octanol and to the membrane/water interface. Peptide-induced efflux became faster as the Gibbs energies for binding and insertion of the tp10 variants decreased. If anionic lipids were included, binding and efflux rate increased, as expected because all tp10 variants are cationic.
The general transport reaction catalyzed by transportans is:
transportan/cargo (out) transportan/cargo (in)