Earlier this year, Cheng's group developed a method of making helical polypeptides with positively charged side chains. To test whether a helical polypeptide could be an efficient gene delivery agent, the group assembled a library of 31 helical polypeptides that are stable over a broad pH range and can bond to DNA for delivery. Most of them outperformed PLL and a few outstripped a leading commercial agent called polyethyleneimine (PEI), notorious for its toxicity although it is highly efficient. The helical molecules even worked on some of the hardest cells to transfect: stem cells and fibroblast cells.
"People kind of gave up on polypeptide-based materials for gene deliveries because PLL had low efficiency and high toxicity," Cheng said. "The polypeptide that we designed, synthesized and used in this study has very high efficiency and also well-controlled toxicities. With a modified helical polypeptide, we demonstrated that we can outperform many commercial agents."
The polypeptides Cheng and his co-workers developed can adopt helical shapes because the side chains are longer, so that the positive charges do not interfere with the protein's winding. The positive charges readily bind to negatively charged DNA, forming complexes that are internalized into cellular compartments called endosomes. The helical structures rupture the endosomal membranes, letting the DNA escape into the cell.
To confirm that the spiral polypeptide shape is the key to transfection, the researchers then synthesized two batches of the most efficient polypeptide: one batch with a helical shape, one with the usual random coil. The helical polypeptide far exceeded the random-
|Contact: Liz Ahlberg|
University of Illinois at Urbana-Champaign