Noncationic Rigid and Anisotropic Coiled-Coil Proteins Exhibit Cell-Penetration Activity

Significance Statement

The use of cationic polymers and cationic cell-penetrating peptides as non-viral carriers in cellular delivery systems has been studied, but polycations are usually faced with the problems such as inflammatory nature and cytotoxicity. Researchers in Japan, Nippon Institute of Technology, RIKEN, and Hokkaido University have previously reported that artificial proteins having rigid and anisotropic structure and surface cationic property showed superior cell-penetrating activities. In this report, the authors designed novel artificial protein variants of rigid and anisotropic structure but noncationic surface to avoid problems related to inflammation and cytotoxicity. These artificial proteins showed less cell-penetrating activity than previous cationic artificial protein, however, they were able to penetrate cells comparable to cationic cell-penetrating peptides. Further, one variant did not show short-term cytotoxicity in all the cells tested. These findings provide new insights for the design of non-viral and non-cationic carriers in cellular delivery systems with excellent efficacy and safety.

About the author

Ken-Ichi Sano is an associate professor of Innovative Systems Engineering at Nippon Institute of Technology. He received his PhD from Nagoya University and was a postdoctoral fellow at RIKEN in SPring-8, Cancer Institute Japanese Foundation for Cancer Research, and was a Deputy Unit Leader at RIKEN in Wako. He was the recipient of the Lewis Dienes Award of the 10th International Organization of Mycoplasmology, and the Young Investigator Award of the 4th International Peptide Meeting. His current research interests include cellular drug delivery systems, evaluation of antidepressant agents using novel model systems, and creation of functional artificial proteins.

Journal Reference

Langmuir. 2015;31(30):8218-23.

Nakayama N1, Hagiwara K1,2, Ito Y1, Ijiro K1,3, Osada Y1, Sano K1. 

[expand title=”Show Affiliations”]
  1. Nano Medical Engineering Laboratory, RIKEN, Wako, Saitama 351-0198, Japan.
  2. Tokyo Metropolitan Institute of Medical Science, Setagaya, Tokyo 156-8506, Japan.
  3. Research Institute for Electronic Science, Hokkaido University, Sapporo, Hokkaido 001-0021, Japan [/expand].


Numerous cationic peptides that penetrate cells have been studied intensively as drug delivery system carriers for cellular delivery. However, cationic molecules tend to be cytotoxic and cause inflammation, and their stability in the blood is usually low. We have previously demonstrated that a rigid and fibrous cationic coiled-coil protein exhibited cell-penetrating ability superior to that of previously reported cell-penetrating peptides. Making use of structural properties, here we describe the cell-penetrating activity of a rigid and fibrous coiled-coil protein with a noncationic surface. A fibrous coiled-coil protein of pI 6.5 penetrated 100% of the cells tested in vitro at a concentration of 500 nM, which is comparable to that of previously reported cell-penetrating peptides. We also investigated the effect of cell-strain dependency and short-term cytotoxicity.

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Figure Legend: Summary of cell-penetrating activity of artificial protein having rigid and anisotropic structure with various surface properties.


Noncationic Rigid and anisotropic Coiled-Coil Proteins Exhibit Cell-Penetration Activity. Global Medical Discovery