title: Sequential Order of the Secondary Structure Transitions of Proteins under External Perturbations: Regenerated Silk Fibroin under Thermal Treatment.
abstract: Whether the process of protein folding/unfolding is fully cooperative or it contains sequential elements has long been a fundamental issue in protein science. This issue seemingly became straightforward since the appearance of generalized two-dimensional (2D) correlation spectroscopy in 1990s, because 2D correlation analysis has been considered as a convenient and powerful analytical tool to determine the sequential order of events under external physical or chemical perturbations. In this work, the sequential order of the secondary structure transitions of regenerated silk fibroin under thermal treatment from 130 to 220 °C was first studied using generalized 2D correlation spectroscopy, but an apparently doubtful sequential order was obtained; β-sheet was the first one to change at low temperature, then the random coil, followed by the nonamide C═O and, finally, the α-helix. A subsequent detailed in situ infrared spectral analysis showed that the main secondary structures of silk fibroin, including α-helix, β-turn, random coil and β-sheet (high-wavenumber component), all changed with a fully cooperative manner at a relatively low temperature of 150 °C. But the low-wavenumber component of β-sheet started to change at a higher temperature of 180 °C. Besides, it has also been found that, before 200 °C, the loss of α-helix and random coil was transformed into β-turn, β-sheet, and nonamide C═O. After 200 °C, some β-turn structure was also disruptured and transformed into β-sheet and nonamide C═O.
authors.affiliation: Jiangsu Key Laboratory for the Design and Application of Advanced Functional Polymer, State and Local Joint Engineering Laboratory for Novel Functional Polymeric Materials, College of Chemistry, Chemical Engineering and Materials Science, Soochow University , Suzhou 215123, China.
authors.forename: Zhipeng
authors.initials: Z
authors.lastname: He
authors.affiliation: Jiangsu Key Laboratory for the Design and Application of Advanced Functional Polymer, State and Local Joint Engineering Laboratory for Novel Functional Polymeric Materials, College of Chemistry, Chemical Engineering and Materials Science, Soochow University , Suzhou 215123, China.
authors.forename: Tingting
authors.initials: T
authors.lastname: Zhao
authors.affiliation: Jiangsu Key Laboratory for the Design and Application of Advanced Functional Polymer, State and Local Joint Engineering Laboratory for Novel Functional Polymeric Materials, College of Chemistry, Chemical Engineering and Materials Science, Soochow University , Suzhou 215123, China.
authors.forename: Xiaofeng
authors.initials: X
authors.lastname: Zhou
authors.affiliation: Jiangsu Key Laboratory for the Design and Application of Advanced Functional Polymer, State and Local Joint Engineering Laboratory for Novel Functional Polymeric Materials, College of Chemistry, Chemical Engineering and Materials Science, Soochow University , Suzhou 215123, China.
authors.forename: Zhao
authors.initials: Z
authors.lastname: Liu
authors.affiliation: Jiangsu Key Laboratory for the Design and Application of Advanced Functional Polymer, State and Local Joint Engineering Laboratory for Novel Functional Polymeric Materials, College of Chemistry, Chemical Engineering and Materials Science, Soochow University , Suzhou 215123, China.|Zhangjiagang Institute of Industrial Technologies of Soochow University , Zhangjiagang, 215600, China.
authors.forename: He
authors.identifier: 0000-0002-6547-9193
authors.initials: H
authors.lastname: Huang
mesh_terms: D000577:Amides / Q000737:chemistry; D000818:Animals; D012831:Bombyx / Q000378:metabolism; D005349:Fibroins / Q000737:chemistry*; D006358:Hot Temperature; D017433:Protein Structure, Secondary; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D000577:Amides; D005349:Fibroins