AFM Observation of Protein Nanotubes

Yasumasa Suzuki^1*, Wataru Mizutani², Tsutomu Nakanishi³, Hajime Okamoto³,Yukiko Nagai³, Kyozaburo Takeda³, Ikuo Obataya⁴, Hisakazu Mihara⁴

1) National Institute of Advanced Industrial Science and Technology (AIST)
2) Joint Research Center for Atom Technology-AIST
3) School of Science and Engineering, Waseda University
4) Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology

Protein nanotubes (PNTs) have a hollow tubular structure by self-stacking of cyclopeptides. Modification of those cyclopeptides controls the electronic as well as molecular structure of those PNTs. Here, we focus on the two PNTs whose cyclopeptides are composed of six or eight amino acids, and investigate the morphology by AFM observation. We incubated gold substrates in 0.05 mM dimethylsulfoxide solution of synthesized 6- and 8-cyclopeptide for 2-72 h at 50C, and carried out tapping mode force microscopy observation in air. In the case of 6-cyclopeptide, we found many linear structures with a height of 1.5-2 nm, a length of about 100 nm, and a width of 20 nm. We did not find similar linear structures on the gold substrate immersed in the 8-cyclopeptide solution, but many protruded structures with various heights of 3-7 nm. We assume that the both structures can be the protein nanotubes grown laterally or vertically on the substrate. The change in the growth direction may be due to the different diameter of the rings of the cyclopeptides.

* Present address: Energy Electronics Research Institute