Characterization of unique heavy chain fibroin filaments spun underwater by the caddisfly Stenopsyche marmorata (Trichoptera; Stenopsychidae).

The silks of both Lepidoptera and its sister order Trichoptera contain a homologue of heavy chain (H-fibroin), which is assumed to determine the physical properties of the fiber, such as elasticity and toughness. The long repetitive region of the H-fibroin caddisfly Stenopsyche marmorata shows a conspicuous hierarchical structure that is composed of huge units, which are mainly constructed from four large blocks (SA, SB, SC and SD) arranged in an orderly fashion. Each block contains short, distinct motifs such as SXSXSX(SX), GPXG(X)(1-3) or triplet GGX, which also occur in lepidopteran and spider filaments.