Molecular and Mechanical Properties of Major Ampullate Silk of the Black Widow Spider, Latrodectus hesperus

Molecular and material properties of major ampullate silk were studied for the cobweb-building black widow spider Latrodectus hesperus. Material properties were measured by stretching the silk to breaking. The strength was 1.0 ± 0.2 GPa, and the extensibility was 34 ± 8%. The secondary structure of the major ampullate silk protein was studied using carbon-13 NMR spectroscopy. Alanine undergoes a transition from a coiled structure in pre-spun silk to a beta sheet structure in post-spun silk. We have also isolated two distinct cDNAs (both about 500 bp) which encode proteins similar to major ampullate spidroin 1 and 2 (MaSp1 and MaSp2). The MaSp1-like silk contains polyalanine runs of 5−10 residues as well as GA and GGX motifs. The MaSp2-like silk contains polyalanine runs of varying length as well as GPG(X)<INF>n</INF><INF></INF> motifs. L. hesperus major ampullate silk is more like major ampullate silk from other species than other L. hesperus silks.