TAILIEUCHUNG - Báo cáo khoa học: An investigation into the effect of potassium ions on the folding of silk fibroin studied by generalized two-dimensional NMR–NMR correlation and Raman spectroscopy

We used generalized two-dimensional NMR–NMR correlation to examine the effect of potassium ions on the conformation transition in silk fibroin to investigate the possibility that the fairly high K + ion content found in the distal end of silk-secreting ducts in the silkworms could have a bearing on natural formation of the silk fiber. | ỊFEBS Journal An investigation into the effect of potassium ions on the folding of silk fibroin studied by generalized two-dimensional NMR-NMR correlation and Raman spectroscopy Qing-Xia Ruan Ping Zhou Bing-Wen Hu and Dan Ji The Key Laboratory of Molecular Engineering of Polymers Ministry of Education Department of Macromolecular Science Fudan University Shanghai China Keywords conformation transition generalized twodimensional NMR-NMR correlation potassium ion Raman spectroscopy silk fibroin Correspondence P. Zhou The Key Laboratory of Molecular Engineering of Polymers Ministry of Education Department of Macromolecular Science Fudan University Shanghai 200433 China Fax 86 21 65640293 Tel 86 21 55664038 E-mail pingzhou@ Received 16 October 2007 revised 11 November 2007 accepted 13 November 2007 doi We used generalized two-dimensional NMR-NMR correlation to examine the effect of potassium ions on the conformation transition in silk fibroin to investigate the possibility that the fairly high K ion content found in the distal end of silk-secreting ducts in the silkworms could have a bearing on natural formation of the silk fiber. This has enabled us to propose a detailed mechanism for the transition process. Our evidence indicates that increasing the K from 0 to mg g-1 in the silk fibroin as is thought to occur as the silk fibroin moves through the secretory pathway to the spigot produces a sequence of secondary structural changes helix and or random coil fi helix-like fi b-sheet-like fi b-sheet. The sequence is the same as that produced in silk fibroin films by decreasing the pH of fibroin from to . In addition we used Raman spectroscopy to study the effect of K ions on the Fermi doublet resonance of the tyrosyl phenolic ring at 850 and 830 cm-1. The intensity ratio I850 I830 at these wave numbers indicated that the hydrogen bonding formed by the tyrosyl pheno-lic-OH becomes more stable with an increase in the K

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