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Effect of metallic ions on silk formation in the Mulberry silkworm, Bombyx mori.

Authors
  • Zhou, Li1
  • Chen, Xin
  • Shao, Zhengzhong
  • Huang, Yufang
  • Knight, David P
  • 1 The Key Laboratory of Molecular Engineering of Polymers, Department of Macromolecular Science, National Microanalysis Center, Fudan University, Shanghai, 200433, People's Republic of China. , (China)
Type
Published Article
Journal
The Journal of Physical Chemistry B
Publisher
American Chemical Society
Publication Date
Sep 08, 2005
Volume
109
Issue
35
Pages
16937–16945
Identifiers
PMID: 16853155
Source
Medline
License
Unknown

Abstract

A protein conformation transition from random coil and/or helical conformation to beta-sheet is known to be central to the process used by silk-spinning spiders and insects to convert concentrated protein solutions to tough insoluble threads. Several factors including pH, metallic ions, shear force, and/or elongational flow can initiate this transition in both spiders and silkworms. Here, we report the use of proton induced X-ray emission (PIXE), inductively coupled plasma mass spectroscopy (ICP-MS) and atomic adsorption spectroscopy (AAS) to investigate the concentrations of six metal elements (Na, K, Mg, Ca, Cu, and Zn) at different stages in the silk secretory pathway in the Bombyx mori silkworm. We also report the use of Raman spectra to monitor the effects of these six metallic ions on the conformation transition of natural silk fibroin dope and concentrated regenerated silk fibroin solution at concentrations similar to the natural dope. The results showed that the metal element contents increased from the posterior part to the anterior part of silk gland with the exception of Ca which decreased significantly in the anterior part. We show that these changes in composition can be correlated with (i) the ability of Mg2+, Cu2+, and Zn2+ to induce the conformation transition of silk fibroin to beta-sheet, (ii) the effect of Ca2+ in forming a stable protein network (gel), and (iii) the ability of Na+ and K+ to break down the protein network.

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