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62 Cell-Penetrating Peptides: Processes and Applications
a
b
c
FIGURE 3.2 Coupling of transportan (TP) to different cargoes: (a) thiol group of Cys or
biotin coupled to the side chain of Lys 13 of TP; (b) primary amino group of the cargo protein
or, specifically, a biotin-binding site of streptavidin and biotin antibody; (c) bifunctional crosslinker
covalently coupling Cys in TP with primary amino groups of the cargo protein.
proteins. Thus, the delivery capacity of transportan was estimated using avidin of
about 70 kDa and antibodies of 150 kDa molecular weight.
A bifunctional cross-linker SMCC [succinimidyl-4-(maleimidomethyl)-cyclohexane-1-carboxylate]
34 was used to connect transportan and a cargo protein
(Figure 3.2c), in order to obtain more stable conjugates than the disulfide-bridged
adducts and to avoid the necessity of introducing extra cysteine into the protein to
be delivered.