A Class of Human Proteins that Deliver Functional Proteins into Mammalian Cells In Vitro and In Vivo

Prior studies have shown that the higher the net positive charge a protein has, the more likely it is able to cross the cell membrane. In this article the authors search the human proteome for proteins with the highest positive theoretical charge to molecular weight ratio that could be expressed in E. coli. These proteins, naturally supercharged human proteins (NSHPs), were then fused to reporter constructs and were shown to be able to cross the cell and nuclear membrane of varying cell types. In the figure below, the NSHPs (the six structures shown) and proteins known to penetrate the cell membrane (bottom 3 and +36 GFP) are fused to mCherry and incubated with 3 cell types. The median fluorescence is then determined by flow cytometry.