Characterization of the second type of aciniform spidroin (AcSp2) provides new insight into design for spidroin-based biomaterials

Spiders spin a range of silks from different glands for distinct functions, and each silk type exhibits distinct material properties. Silk extruded by the aciniform gland is used for prey wrapping and egg case construction and displays high toughness and extensibility. So far, only the aciniform spidroin 1 (AcSp1) gene which was firstly identified as a silk gene in aciniform gland has been obtained. Here we present the gene sequence for the second type of full-length aciniform silk protein, AcSp2. Analysis of the AcSp2 primary sequence reveals relatively conserved terminal regions and a distinct repetitive sequence relative to AcSp1. A fraction of the gene can be expressed in recombinant systems. Secondary structure analysis of the recombinant AcSp2 protein in solution reveals that the protein adopts mainly an α-helical conformation. Artificial spinning of recombinant AcSp2 demonstrates that the spidroins can be spun into fine fibers which display up to 142% extensibility. The silk fibers are dominated by β-sheet and β-turn secondary structures. Moreover, the mechanical data collected from these synthetic fibers revealed that the mechanical properties are partly correlated with the molecular weights. Overall, our studies enrich our knowledge of spidroin gene family members and provide a new insight into creation of high-performance silk fibers for next generation biomaterials.