Study on Self-assembled Giant Nanosheets from Tyrosine-containing Helical Peptides

Abstract

One of the important challenges in the development of protein-mimetic materials is to understand the sequence specific assembly behavior and the dynamic folding change. Conventional strategies to construct two dimensional nanostructures from the peptides have been limited to β-sheet forming sequences in use of basic building blocks because of their natural tendency to form sheet like aggregations. In this study a new sequence of tyrosine containing peptide was identified, which can form dimers by the disulfide bridge, fold into helix and assemble into macroscopic flat sheet at the air/water interface. We found that stabilization of helix by the dimerization is a key determinant for maintaining macroscopic flatness. Proton conduction in biological systems has been an important issue for a better understanding of fundamental life mechanism. In representative proton transfer systems in organisms such as a proton translocation in mitochondria and a proton coupled electron transfer (PCET) of photosystem, it was turned out that several amino acids take an active part as proton transporters. Especially, tyrosine has been known to play a critical role in PCET interplaying with a Ca-Mn cluster in the photosystem II. Moreover it can be polymerized into cross-linked polymers, melanin, possessing a semiconductor-like behavior dependent on hydration. Inspired from this, we made proton conductor with tyrosine containing 2D peptide material by hybridization with inorganic species via the tyrosine oxidation reaction. It was expected to combine the conventional role of tyrosine as a building block of self-assembled structures with the mediating ability as proton conductor. In this process, our attempt also shows that functionalization and/or modification of 2D peptide films can be done through a simple secondary treatment. In perspective of bioelectronics and further applications, it would be a good example for designing versatile platforms for bio-functionalized devices with biocompatible materials.