Exceptional mechanical stability of the spider silk C-terminal domain

Abstract

The helical C-terminal domain (CTD) of spider silk proteins exhibits exceptionally high mechanical stability, with an unfolding force of ~110 pN, challenging the conventional view that helical proteins are mechanically weak. Two distinct stepwise unfolding pathways (11 nm + 35 nm, 19 nm + 28 nm) of CTD are identified. Dynamic force spectroscopy further revealed that the CTD becomes structurally unstable under acidic conditions (pH 5.7), reflecting its functional role in the spinning process. These findings advance our understanding of spider silk protein mechanics and provides new insights into the relationship between structure and mechanics.