A comparison of convergently evolved insect silks that share β-sheet molecular structure

Abstract

Raspy crickets produce silk webs that are used to build shelters. These webs have been found to consist of both fiber and film components. Raman spectra obtained from both components were found to be very similar for a given species. The protein structure of the fibers and films produced by both species was predominately β-sheet with lesser amounts of β-turns, unordered and α-helical protein also detected. The orientation of the β-sheet backbone in the fiber was determined to be parallel to the fiber axis. Compared to cocoon and dragline silk the orientation distribution exhibits a significant randomly orientated protein component. Amino acid analysis confirmed the presence of glycine, serine, and alanine in both species, which are known to form antiparallel β-sheet structures. Both species, although at significantly different concentrations, where found to contain proline. This amino acid is uncommon in insect silks, and likely involved in increasing fiber elasticity.

Keywords: Raman spectroscopy; amino acid composition; protein conformation; protein orientation; silk.