Effects of Mini-Spidroin\nRepeat Region on the Mechanical\nProperties of Artificial Spider Silk Fibers

Spiders can produce up to seven different types of silk,\neach with\nunique mechanical properties that stem from variations in the repetitive\nregions of spider silk proteins (spidroins). Artificial spider silk\ncan be made from mini-spidroins in an all-aqueous-based spinning process,\nbut the strongest fibers seldom reach more than 25% of the strength\nof native silk fibers. With the aim to improve the mechanical properties\nof silk fibers made from mini-spidroins and to understand the relationship\nbetween the protein design and the mechanical properties of the fibers,\nwe designed 16 new spidroins, ranging from 31.7 to 59.5 kDa, that\nfeature the globular spidroin N- and C-terminal domains, but harbor\ndifferent repetitive sequences. We found that more than 50% of these\nconstructs could be spun by extruding them into low-pH aqueous buffer\nand that the best fibers were produced from proteins whose repeat\nregions were derived from major ampullate spidroin 4 (MaSp4) and elastin.\nThe mechanical properties differed between fiber types but did not\ncorrelate with the expected properties based on the origin of the\nrepeats, suggesting that additional factors beyond protein design\nimpact the properties of the fibers.