Sequence Identification, Recombinant Production, and Analysis of the Self-Assembly of Egg Stalk Silk Proteins from Lacewing Chrysoperla carnea.

Martin Neuenfeldt,Thomas Scheibel

doi:10.3390/biom7020043

Abstract

Egg stalk silks of the common green lacewing Chrysoperla carnea likely comprise at least three different silk proteins. Based on the natural spinning process, it was hypothesized that these proteins self-assemble without shear stress, as adult lacewings do not use a spinneret. To examine this, the first sequence identification and determination of the gene expression profile of several silk proteins and various transcript variants thereof was conducted, and then the three major proteins were recombinantly produced in Escherichia coli encoded by their native complementary DNA (cDNA) sequences. Circular dichroism measurements indicated that the silk proteins in aqueous solutions had a mainly intrinsically disordered structure. The largest silk protein, which we named ChryC1, exhibited a lower critical solution temperature (LCST) behavior and self-assembled into fibers or film morphologies, depending on the conditions used. The second silk protein, ChryC2, self-assembled into nanofibrils and subsequently formed hydrogels. Circular dichroism and Fourier transform infrared spectroscopy confirmed conformational changes of both proteins into beta sheet rich structures upon assembly. ChryC3 did not self-assemble into any morphology under the tested conditions. Thereby, through this work, it could be shown that recombinant lacewing silk proteins can be produced and further used for studying the fiber formation of lacewing egg stalks.

Highlights

Oviposition, a unique egg laying behavior exhibited by most species of female lacewings, results in the production of an egg attached to an egg stalk comprised primarily of silk proteins [1]
Egg stalk silks from several lacewing species have been investigated in terms of amino acid composition and concerning structural properties of the fibers [4,10], protein sequence information is only available for two egg stalk proteins of the Australian species M. signata [6]
In order to evaluate sequence homologies of egg stalks to a related European member of the family Chrysopidae (Figure S7), silk-encoding complementary DNA sequences of Chrysoperla carnea were identified using primers based on nucleotide sequences of MalXB1 and MalXB2, respectively

Summary

Introduction

Oviposition, a unique egg laying behavior exhibited by most species of female lacewings, results in the production of an egg attached to an egg stalk comprised primarily of silk proteins [1]. Silk proteins are typically associated with arthropods, like silkworms or spiders; lacewings have several interesting and unique aspects to their silk proteins and their processing. The resulting egg stalk protects the egg from predators and cannibalism by lifting it from the ground until the larva hatches [1]. This key difference in silk processing, when comparing most arthropods to lacewing silk, indicates that some form of pre-assembly of the proteins in solution must occur. This makes lacewing silk a interesting tool to study the self-assembly behavior of silk proteins

Methods

Results

Conclusion