title: Conformation transition in silk protein films monitored by time-resolved Fourier transform infrared spectroscopy: effect of potassium ions on Nephila spidroin films.
abstract: We used time-resolved Fourier transform infrared spectroscopy (FTIR) to follow a conformation transition in Nephila spidroin film from random coil and/or helical structures to beta-sheet induced by the addition of KCl from 0.01 to 1.0 mol/L in D(2)O. Time series difference spectra showed parallel increases in absorption at 1620 and 1691 cm(-)(1), indicating formation of beta-sheet, together with a coincident loss of intensity of approximately 1650 cm(-)(1), indicating decrease of random coil and/or helical structures. Increase in KCl concentration produced an increased rate of the conformation transition that may attributable to weakening of hydrogen bonds within spidroin macromolecules. The conformation transition was a biphasic process with [KCl] > or = 0.3 mol/L but monophasic with [KCl] < or = 0.1 mol/L. This suggests that, at high KCl concentrations, segments of the molecular chain are adjusted first and then the whole molecule undergoes rearrangement. We discuss the possible significance of these findings to an understanding of the way that spiders spin silk.
authors.affiliation: Department of Macromolecular Science, The Key Laboratory of Molecular Engineering of Polymers of Education Ministry, Fudan University, Shanghai 200433, People's Republic of China. chenx@fudan.edu.cn
authors.forename: Xin
authors.initials: X
authors.lastname: Chen
authors.forename: David P
authors.initials: DP
authors.lastname: Knight
authors.forename: Zhengzhong
authors.initials: Z
authors.lastname: Shao
authors.forename: Fritz
authors.initials: F
authors.lastname: Vollrath
mesh_terms: D000818:Animals; D002414:Cations, Monovalent / Q000737:chemistry; D017666:Deuterium Oxide / Q000737:chemistry; D005349:Fibroins; D019476:Insect Proteins; D007700:Kinetics; D011188:Potassium / Q000737:chemistry*; D011189:Potassium Chloride / Q000737:chemistry; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D011506:Proteins / Q000737:chemistry*; D047011:Silk; D012996:Solutions; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods; D013112:Spiders / Q000737:chemistry*; D013696:Temperature; D013997:Time Factors
chemical_list: D002414:Cations, Monovalent; D019476:Insect Proteins; D011506:Proteins; D047011:Silk; D012996:Solutions; C086087:spidroin 1; D011189:Potassium Chloride; D005349:Fibroins; D017666:Deuterium Oxide; D011188:Potassium