Structure - Property and Structure - Function Relations of Leafhopper (Kahaono montana) Silk

Abstract

Kahaono montana Evans (Insecta: Hemiptera: Cicadellidae), an endemic Australian leafhopper, is unique among the insect order Hemiptera in producing a silk. In this study, the secondary structure of the protein comprising leafhopper silk, and the surface stretching mechanical properties of this biopolymer, were investigated using Fourier-transform infrared microscopy and atomic force microscopy, respectively. The curve-fitted amide I and amide III bands revealed a composition of 13.1% α-helix, 23.8% β-sheet, 25.5% random coil, and 37.6% aggregated side chains. The molecular stretching behaviour of raw and cleaned silk fibres differed markedly. Analysis of the AFM force curves showed an adhesive property of the raw silk, while the pure fibre showed only the presence of protein. These findings suggest that the silk fibres act as a structural support for other leafhopper secretions and together form a hydrophobic barrier that may protect the insects from rain and natural enemies. This is the first time such a use of silk has been found in a biological system.