Mechanical and structural features of three AcSp proteins underlie the diverse material properties of aciniform silks of Neoscona spiders

Spider silks are desirable multicomponent biomaterials characterized by great tensile strength, extensibility, and biocompatibility. Of all spider silk types, aciniform silk has highest toughness due to its combination of high tensile strength and elsticity. Here, we identify three major spidroin components (AcSp1A, AcSp1B, and AcSp2) from aciniform silk of orbweb weaving spider, Neoscona scylloides, and present their full-length coding gene sequences. Comparative sequence and expression level analysis show that AcSp1B has highest expression level and higher serine content than other two AcSp proteins, while the AcSp2 shows very low mRNA level. Furthermore, three recombinant minimalist AcSp proteins are produced and could be induced to form fibers by shear forces in a physiological buffer. The manual-drawn AcSp1B fiber shows strongest tensile strength among three AcSp fibers because of its higher β-sheet formed by abundant serine content. We also compare mechanical properties of aciniform silks between two Neoscona species (N. theisi and N. scylloides) and found that aciniform silks from N. theisi exhibit higher tensile strength than those of N. scylloides, which may result from altering expression levels of two AcSp1 proteins. Collectively, our results provide insights into the mechanical features of each component in aciniform silk from N. scylloides and reveal the molecular mechanism of diverse material properties of aciniform silk among species.