Triangle weaver spiders construct spring-loaded webs using a novel set of genes for exceptionally proline-rich silk

Spiders amplify their physical capabilities by synthesizing multiple high performing silks. Renowned for its toughness, major ampullate (MA) silk composes the spiderweb frame, providing support and absorbing high-energy impacts. In ecribellate orb-weavers, proline-rich motifs in MaSp2 proteins of MA silk are linked to a range of mechanical properties, including extensibility, elasticity, stiffness, and supercontraction. We show a modification of these motifs outside of this clade in a spider that constructs a spring-loaded web. The triangle weaver spider <i>Hyptiotes cavatus</i> (family Uloboridae) stores energy in the support lines of its triangular web, then rapidly releases the tension to catapult forward, collapsing the web around prey. <i>Hyptiotes</i> has an expanded set of <i>MaSp2</i> genes which encode proteins with far higher proline contents than typical MaSp2. The predominant GPGPQ motifs present in <i>Hyptiotes</i> spidroins also occur abundantly in MaSp sequences of distantly related spiders that produce the most extensible dragline, implying silk protein convergence. Proline-rich MaSp2 proteins constitute half of all MA gland expression in <i>Hyptiotes</i>, and we show that the resulting fibers are the most proline-rich spider silk measured to date. This unique silk composition suggests a functional importance that may facilitate the spring-loaded prey capture mechanism of this species' web and may inspire the design of novel biomaterials using protein engineering.