A class of human proteins that deliver functional proteins into mammalian cells in vitro and in vivo

Abstract

We discovered a class of naturally occurring human proteins with unusually high net positive charge that can potently deliver proteins in functional form into mammalian cells both in vitro and also in murine retina, pancreas, and white adipose tissues in vivo. These findings represent diverse macromolecule delivery agents for in vivo applications, and also raise the possibility that some of these human proteins may penetrate cells as part of their native biological functions.

Figure 1. Naturally supercharged human proteins (NSHPs) penetrate mammalian cells in vitro

(A) Plot of human proteins expressed from E. coli within the Protein Data Bank. The blue dots represent proteins with positive charge:molecular weight ratios exceeding +0.75/kDa. (B) Median mCherry fluorescence of HeLa, 3T3 and BSR cells incubated with NSHP-mCherry fusions as measured by flow cytometry. (C) NSHP-mCherry fusions (300 nM) were incubated with HeLa cells for 4 hours with increasing concentrations of +36 GFP. After incubation, cells were washed with heparin PBS and internalized NSHP-mCherry was quantified by flow cytometry. For each fusion protein, the percentage of mCherry fluorescence relative to the mCherry intensity without +36 GFP is shown. The co-incubation experiment was also performed with 10 μg/mLtransferrin-Alexa568 (shown in black), which is internalized through an independent mechanism. See also Figure S1.

Figure 2. Naturally supercharged human proteins (NSHPs) deliver active protein into mammalian cells in vitro

(A) Live-cell fluorescence microscopy of floxed tdTomato BSR cells two days after incubation for 4 hours with 2 μM NSHP-Cre fusions. The scale bar is 200 μm. (B) Percent recombined cells among floxed tdTomato BSR cells incubated with NSHP-Cre fusions as measured by flow cytometry. See also Figure S2.

Figure 3. Naturally supercharged human proteins (NSHPs) deliver active proteins into three adult murine tissues in vivo

(A) Adult floxed LacZ mice were injected subretinally with Cre fusion proteins. Recombination results in LacZ activity, which was visualized with X-gal stain (blue) three days after injection. (B) Sections of recombined retinae from the samples in (A) reveal that most of the recombination signal arises from Müller glial cells. (C) Adult floxed LacZ mice injected in the pancreas with Cre fusion proteins exhibit recombination in the exocrine tissues as indicated by LacZ immunostaining (red) and LacZ activity assay five days post-injection. (D) Adult floxed luciferase mice injected subcutaneously with Cre fusion proteins exhibit recombination in the white adipose tissue as visualized by luminescence and luciferase activity assay three days post-injection. For (A) and (D), representative results are shown; see Figure S3 for data from additional replicates.