To extend the applicability of our method, we devised another functionalization approach by using GFP fused to twin-streptag oligopeptide sequence (stGFP). Twin-streptag is a 28 amino acids tag having 2 binding sequences for biotin-binding pocket of streptavidin, with a strong affinity (in the range of pM) for the engineered variant of streptavidin -streptactin. We first found that streptactin labeled with DY649 dye was also crosslinking the bt-DNA, but at higher protein concentrations (above 300 nM) than with the streptavidin-biotin system (Figure ). To functionalize the nanogels, we first obtained a stoichiometric complex of stGFP with streptactin and then used it for crosslinking of bt-DNA (Figure and Figure ). We found that even more stGFP-streptactin complex was necessary in this case to produce compact nanogels (around 1000 nM). We then formed the lipoproplexes with the stGFP-NG-649, incubated them to B16 cells and imaged them by confocal microscopy (Figure ). Here again, fluorescent spots with colocalized fluorescence from streptactin (red) and GFP fluorescence (green) were found inside the cells when they were treated with stGFP-LPX-649 (Figure ). These results expand the functionalizability of DNA-streptavidin (or DNA-streptactin) nanogels and demonstrate that nanogel-based approach for intracellular protein delivery can also be also applicable for cloned proteins bearing not biotin, but specific oligopeptide tags.