Conformation transition of silk protein membranes monitored by time-resolved FTIR spectroscopy: Effect of alkali metal ions on Nephila spidroin membrane

The conformation transition processes of Nephila spidroin membranes induced by alkali salt solutions were monitored by time-resolved FTIR spectroscopy. Though the transition rate of spidroin in the membrane was NaCl > KCl > LiCl, the β-sheet structure content in the membrane ( after the conformation transition completed) was KCl > LiCl > NaCl. Comparing the transition rate and final β-sheet structure content in the membrane, KCl has the best effect in inducing the conformation transition of spidroin membrane among the three alkali salts we used. This supports the assumption that the K+ ions play an important role in the spinning process of spiders. In the meantime, the conformation transition process was indicated to have two intermediate states that contain different levels of β-sheet structure. The first phase (fast phase, with a time constant of ∼5 min) was assigned to the β-sheet formation by segments movement, while the second phase (slow phase, with a time constant of β50 min) was attributed to the whole macromolecular rearrangement.