Lacewing Surprises With Two Kinds Of Silk

The green lacewing (Mallada signata) makes two kinds of silk proteins, Australian researchers have found (Biomacromolecules, DOI: 10.1021/bm8005853). Although spiders make as many as seven different kinds of silk, this is the first example of an insect that makes more than one silk. Female lacewings make egg stalks—a fiber strand that supports an egg—from a well-characterized serine-rich protein that has a cross-β-sheet structure. Larvae of both sexes pupate in a silk cocoon, but scientists haven't known if the cocoon silk is the same material as the egg-stalk silk. Tara D. Sutherland and coworkers at CSIRO, the Australian national science agency, now report that the two silks are chemically quite different. The cocoon silk, which they call MalFibroin (for Mallada signata fibroin), is a 49-kilodalton, alanine-rich protein with a predominantly α-helical structure. The cocoon's outer layer consists of a loose mesh of the fiber, whereas in the inner layer the fiber acts as a scaffold for a mixture of waterproofing lipids.