Probing the Impact of Acidification on Spider Silk Assembly Kinetics.

Spiders utilize fine adjustment of the physicochemical conditions within its silk spinning system to regulate spidroin assembly into solid silk fibers with outstanding mechanical properties. However, the exact mechanism about which this occurs remains elusive and is still hotly debated. In this study, the effect of acidification on spider silk assembly was investigated on native spidroins from the major ampullate (MA) gland fluid excised from Latrodectus hesperus (Black Widow) spiders. Incubating the protein-rich MA silk gland fluid at acidic pH conditions results in the formation of silk fibers that are 10–100 μm in length and ∼2 μm in diameter as judged by optical and electron microscope methods. The in vitro spider silk assembly kinetics were monitored as a function of pH with a 13C solid-state MAS NMR approach. The results confirm the importance of acidic pH in the spider silk self-assembly process with observation of a sigmoidal nucleation-elongation kinetic profile. The rates of nucleation and elong...