title: In vivo effects of metal ions on conformation and mechanical performance of silkworm silks.
abstract: The mechanism of silk fiber formation is of particular interest. Although in vitro evidence has shown that metal ions affect conformational transitions of silks, the in vivo effects of metal ions on silk conformations and mechanical performance are still unclear.
  
  
  
  This study explored the effects of metal ions on silk conformations and mechanical properties of silk fibers by adding K+and Cu2+into the silk fibroin solutions or injecting them into the silkworms. Aimed by CD analysis, FTIR analysis, and mechanical testing, the conformational and mechanical changes of the silks were estimated. By using BION Web Server, the interactions of K+and N-terminal of silk fibroin were also simulated.
  
  
  
  We presented that K+and Cu2+induced the conformational transitions of silk fibroin by forming β-sheet structures. Moreover, the mechanical parameters of silk fibers, such as strength, toughness and Young's modulus, were also improved after K+or Cu2+injection. Using BION Web Server, we found that potassium ions may have strong electrostatic interactions with the negatively charged residues.
  
  
  
  We suggest that K+and Cu2+play crucial roles in the conformation and mechanical performances of silks and they are involved in the silk fiber formation in vivo.
  
  
  
  Our results are helpful for clarifying the mechanism of silk fiber formation, and provide insights for modifying the mechanical properties of silk fibers.
authors.affiliation: State Key Laboratory of Silkworm Genome Biology, Southwest University, Chongqing 400716, PR China; Chongqing Engineering and Technology Research Center for Novel Silk Materials, Southwest University, Chongqing 400716, PR China.
authors.forename: Xin
authors.initials: X
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Silkworm Genome Biology, Southwest University, Chongqing 400716, PR China.
authors.forename: Yi
authors.initials: Y
authors.lastname: Li
authors.affiliation: State Key Laboratory of Silkworm Genome Biology, Southwest University, Chongqing 400716, PR China.
authors.forename: Qingsong
authors.initials: Q
authors.lastname: Liu
authors.affiliation: Department of Biochemistry and Molecular Biology, Chongqing Medical University, Chongqing 400016, PR China.
authors.forename: Quanmei
authors.initials: Q
authors.lastname: Chen
authors.affiliation: State Key Laboratory of Silkworm Genome Biology, Southwest University, Chongqing 400716, PR China; Chongqing Engineering and Technology Research Center for Novel Silk Materials, Southwest University, Chongqing 400716, PR China.
authors.forename: Qingyou
authors.initials: Q
authors.lastname: Xia
authors.affiliation: State Key Laboratory of Silkworm Genome Biology, Southwest University, Chongqing 400716, PR China; Chongqing Engineering and Technology Research Center for Novel Silk Materials, Southwest University, Chongqing 400716, PR China. Electronic address: zhaop@swu.edu.cn.
authors.forename: Ping
authors.initials: P
authors.lastname: Zhao
mesh_terms: D000818:Animals; D012831:Bombyx / Q000378:metabolism*; D055119:Elastic Modulus; D007477:Ions / Q000378:metabolism*; D008670:Metals / Q000378:metabolism*; D000072757:Protein Conformation, beta-Strand; D047011:Silk / Q000378:metabolism*
chemical_list: D007477:Ions; D008670:Metals; D047011:Silk
keywords: Conformational transition; Mechanical performance; Metal ions; Silk fiber formation; β-Sheet