title: Ca2+ and endoplasmic reticulum Ca2+-ATPase regulate the formation of silk fibers with favorable mechanical properties.
abstract: Calcium ions (Ca(2+)) are crucial for the conformational transition of silk fibroin in vitro, and silk fibroin conformations correlate with the mechanical properties of silk fibers. To investigate the relationship between Ca(2+) and mechanical properties of silk fibers, CaCl2 was injected into silkworms (Bombyx mori). Fourier-transform infrared spectroscopy (FTIR) analysis and mechanical testing revealed that injection of CaCl2 solution (7.5mg/g body weight) significantly increased the levels of α-helix and random coil structures of silk proteins. In addition, extension of silk fibers increased after CaCl2 injection. In mammals, sarcoplasmic reticulum Ca(2+)-ATPase in muscle and endoplasmic reticulum Ca(2+)-ATPase in other tissues (together denoted by SERCA) are responsible for calcium balance. Therefore, we analyzed the expression pattern of silkworm SERCA (BmSERCA) in silk glands and found that BmSERCA was abundant in the anterior silk gland (ASG). After injection of thapsigargin (TG) to block SERCA activity, silkworms showed a silk-spinning deficiency and their cocoons had higher calcium content compared to that of controls. Moreover, FTIR analysis revealed that the levels of α-helix and β-sheet structures increased in silk fibers from TG-injected silkworms compared to controls. The results provide evidence that BmSERCA has a key function in calcium transportation in ASG that is related to maintaining a suitable ionic environment. This ionic environment with a proper Ca(2+) concentration is crucial for the formation of silk fibers with favorable mechanical performances.
authors.affiliation: State Key Laboratory of Silkworm Genome Biology, Southwest University, Chongqing 400716, China. Electronic address: wangxin3@swu.edu.cn.
authors.forename: Xin
authors.initials: X
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Silkworm Genome Biology, Southwest University, Chongqing 400716, China. Electronic address: liy7raul@swu.edu.cn.
authors.forename: Yi
authors.initials: Y
authors.lastname: Li
authors.affiliation: State Key Laboratory of Silkworm Genome Biology, Southwest University, Chongqing 400716, China. Electronic address: xiekanglwdd@163.com.
authors.forename: Kang
authors.initials: K
authors.lastname: Xie
authors.affiliation: Animal Center, Chongqing Medical University, Chongqing 400016, China. Electronic address: yiqiying_2011@yahoo.com.
authors.forename: Qiying
authors.initials: Q
authors.lastname: Yi
authors.affiliation: State Key Laboratory of Silkworm Genome Biology, Southwest University, Chongqing 400716, China. Electronic address: eidoloncqm@126.com.
authors.forename: Quanmei
authors.initials: Q
authors.lastname: Chen
authors.affiliation: State Key Laboratory of Silkworm Genome Biology, Southwest University, Chongqing 400716, China. Electronic address: wangxiaohuan1024@126.com.
authors.forename: Xiaohuan
authors.initials: X
authors.lastname: Wang
authors.affiliation: College of Resources and Environments, Southwest University, Chongqing 400716, China. Electronic address: shenhong@swu.edu.cn.
authors.forename: Hong
authors.initials: H
authors.lastname: Shen
authors.affiliation: State Key Laboratory of Silkworm Genome Biology, Southwest University, Chongqing 400716, China. Electronic address: xiaqy@swu.edu.cn.
authors.forename: Qingyou
authors.initials: Q
authors.lastname: Xia
authors.affiliation: State Key Laboratory of Silkworm Genome Biology, Southwest University, Chongqing 400716, China. Electronic address: zhaop@swu.edu.cn.
authors.forename: Ping
authors.initials: P
authors.lastname: Zhao
mesh_terms: D000818:Animals; D012831:Bombyx / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002122:Calcium Chloride / Q000378:metabolism; D055595:Mechanical Phenomena; D017433:Protein Structure, Secondary; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000378:metabolism*; D047011:Silk / Q000096:biosynthesis / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D047011:Silk; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D002122:Calcium Chloride; D002118:Calcium
keywords: Calcium ion; Endoplasmic reticulum Ca(2+)-ATPase; FTIR; Mechanical properties; Silk fibers