crc press - E-Lib FK UWKS

72 Cell-Penetrating Peptides: Processes and Applications
L2 A13 L6 L8 L15 L4 L11 A18 A7 A14 A3 L17 A10 K5 K12 K16 K9 K1 A2 A13 K6 A8 L15 K4 L11 A18 A7 K14 L3 L17 A10 L5 L12 K16 L9 K1 I II
FIGURE 4.1 Helical wheel projections of the amphipathic and nonamphipathic peptide pairs
I and II.
ABSTRACT
The term MAPs (model amphipathic peptides) designates a group of peptides derived
from the α-helical amphipathic model peptide KLALKLALKALKAALKLA-NH 2,
which is taken up by mammalian cells in a nonendocytic way. The mechanism of
the cellular uptake of MAPs proved to be highly complex and involves energydependent
as well as -independent processes to a comparable extent. Stepwise
structural alterations with respect to chain length, charge, and helix parameters failed
to provide information about essential structural requirements for the cellular uptake
of MAP. Instead, evidence was found for a structure-independent cellular uptake of
all investigated peptides, an enrichment within the cell of amphipathic members of
the series, and a rapid washout of the nonamphipathic ones. Extensive translocation
into the cell interior was also found for disulfide-bridged peptide and phosphorothioate
oligonucleotide conjugates with MAPs. However, no improvement with respect
to the cellular uptake of naked oligonucleotides was observed for the peptide–phosphorothioate
oligonucleotide conjugates.
4.1 INTRODUCING HISTORY
The term MAPs (model amphipathic peptides 1 ) designates a group of peptides
derived from the α-helical amphipathic model peptide KLALKLALKAL-
KAALKLA-NH 2 (I, Figure 4.1), originally designed by Steiner et al. 2 and initially
used in our group for biophysical studies on interactions of bioactive helical amphipathic
peptides with lipidic interfaces. 3-7 Throughout the course of these studies
mammalian cells were exposed to the fluorescein-labeled helical amphipathic and
nonamphipathic pair I and II (KALKLKLALALLAKLKLA-NH 2, Figure 4.1) and
to the all-D-amino acid analog and double-D-amino acid analogs of I in order to
obtain information about the influence of amphipathicity on adsorption to the cell
surface.
Confocal laser scanning microscopy (CLSM)-monitoring of these experiments
revealed unexpectedly extensive intracellular fluorescence after exposure to I and