リサイクル

[3K0601-07-01] Biological approach to form silica on chitin using a fusion silicatein

○Kasun Godigamuwa¹, Kazunori Nakashima¹, Souta Tsujitani¹, Satoru Kawasaki¹ (1. Hokkaido University)

The chairman: Hideaki SASAKI (Ehime University)

Keywords:Biomineralization, Biosilica, Hybrid biomaterials, Silica-polymerizing enzyme

High temperatures, harsh pH conditions, and toxic chemicals involved in the conventional synthesis and coating of inorganic polymers limit the fabrication of new generation hybrid materials immobilizing biomolecules such as live cells and enzymes to apply in different fields including bioelectronics, energy generation, and biomedical applications. Silicatein, an enzyme found in siliceous sponges, catalyzes the polymerization of silica under mild conditions, i.e., at room temperature and neutral pH. We have successfully solved the unfavorable aggregation of silicatein that cause difficulties in handling, by fusing with a small soluble tag called InaKC, a hydrophilic protein from Pseudomonas syringae. Chitin is a biocompatible polymer used in biomedical applications and chitin-binding domain (ChBD) found in chitinase enzyme is a promising anchor that can be used to immobilize enzymes on chitin. The objective of this study is to design a three-component interfacial catalyst containing InaKC, ChBD and silicatein, which can bind on chitin to catalyze silica formation on chitin.
The designed fusion silicatein, InakC-ChBD-Sil was expressed in Escherichia coli and was purified, followed by refolding. Solubility, silica polymerizing activity and adsorption on chitin were investigated. Recovered chitin subjected to silica formation with and without adsorption (control) of fusion silicatein were analyzed by scanning electron microscope (SEM) with energy dispersive X-rays spectroscopy (EDS) analysis.
InaKC-ChBD-Sil maintained its solubility for 24 h and the removal of soluble tags led to aggregate within 1 h. InaKC-ChBD-Sil showed a similar silica polymerization activity to mature silicatein in a solution. InaKC-ChBD-Sil strongly bound on chitin material within 1.0 h. SEM-EDS analysis showed the formation of silica on chitin treated with InaKC-ChBD-Sil while there was no silica formation in the control. These results revealed that the InaKC-ChBD-Sil can be used as an interfacial catalyst to form silica on the chitin under mild conditions.