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Biophysical Studies of Cell-Penetrating Peptides 225
TABLE 10.1
Sequences of Selected Cell-Penetrating Peptides and
Nonpenetrating Analogs
Name Sequence Translocation
Protein-derived
Penetratin, pAntp RQIKIWFQNRRMKWKK yes 4
Nonpenetratin RQIKIFFQNRRMKFKK no 14
pIsl1 RVIRVWFQNKRCKDKK yes 7
Tat-derived YGRKKRRQKKK yes 3
Peptide-derived chimera
Transportan GWTLNSAGYLLGKINLKALAALAKKIL yes 8
Nontransportan LLGKINLKALAALAKKIL no 15
Signal-NLS MGLGLHLLVLAAALQGAKKKRKVC yes 12
GALFLGWLGAAGSTMGAWSQPKKKRKVC yes 13
AAVALLPAVLLALLAPAAANYKKPKL yes 11
Note: Terminal groups may be substituted. Positively charged residues are underlined.
venom mastoparan. 8 The Tat sequence in Table 10.1 is derived from the HIV-1 Tat
protein. 3 This protein was in fact the first example of a protein discovered to be
translocated into cells. 9,10 The NLS-chimera peptides included in Table 10.1 are
derived from hydrophobic parts of different signal peptide sequences fused with
some nuclear localization sequence (NLS). 11-13
Both the pAntp and transportan sequences have variants that have lost their
translocating property, and selected nontransporting variants are also included in
Table 10.1. With penetratin, critical substitutions of two residues — changing Trp
into Phe — is enough to yield a nontransporting peptide. 14 With transportan, successive
deletions from the N terminus showed that a peptide where residues 1–9
had been deleted had essentially lost its translocating property. 15
There is no clear-cut biophysical difference between CCP and non-CPP variants
of the peptides. The common denominator for all the peptides presented in Table 10.1
is that they are, more or less, positively charged at pH 7. In the case of chimeric
CPPs, the charges are localized at the C-terminal part and originate from either an
NLS-moiety or mastoparan (with transportan). The chimera have long stretches of
hydrophobic residues (with no charges) at their N-terminal parts.
10.3 BIOMEMBRANE MIMETIC SOLVENTS AND MODEL SYSTEMS
CPPs are incorporated into any cell type and, today, the only common denominator
is the ability to translocate through the plasma membrane. Transport studies are
preferentially carried out with intact cells, using various microscopic techniques.
However, the complexity of a biological cell and its handling make it difficult, or
impossible, to apply other biophysical methods in a meaningful way. Hence, a more
detailed biophysical molecular understanding requires studies with simplified model