title: Dragline silk: a fiber assembled with low-molecular-weight cysteine-rich proteins.
abstract: Dragline silk has been proposed to contain two main protein constituents, MaSp1 and MaSp2. However, the mechanical properties of synthetic spider silks spun from recombinant MaSp1 and MaSp2 proteins have yet to approach natural fibers, implying the natural spinning dope is missing critical factors. Here we report the discovery of novel molecular constituents within the spinning dope that are extruded into dragline silk. Protein studies of the liquid spinning dope from the major ampullate gland, coupled with the analysis of dragline silk fibers using mass spectrometry, demonstrate the presence of a new family of low-molecular-weight cysteine-rich proteins (CRPs) that colocalize with the MA fibroins. Expression of the CRP family members is linked to dragline silk production, specifically MaSp1 and MaSp2 mRNA synthesis. Biochemical data support that CRP molecules are secreted into the spinning dope and assembled into macromolecular complexes via disulfide bond linkages. Sequence analysis supports that CRP molecules share similarities to members that belong to the cystine slipknot superfamily, suggesting that these factors may have evolved to increase fiber toughness by serving as molecular hubs that dissipate large amounts of energy under stress. Collectively, our findings provide molecular details about the components of dragline silk, providing new insight that will advance materials development of synthetic spider silk for industrial applications.
authors.affiliation: Departments of †Biology and §Chemistry, University of the Pacific , Stockton, California 95211, United States.
authors.forename: Thanh
authors.initials: T
authors.lastname: Pham
authors.forename: Tyler
authors.initials: T
authors.lastname: Chuang
authors.forename: Albert
authors.initials: A
authors.lastname: Lin
authors.forename: Hyun
authors.initials: H
authors.lastname: Joo
authors.forename: Jerry
authors.initials: J
authors.lastname: Tsai
authors.forename: Taylor
authors.initials: T
authors.lastname: Crawford
authors.forename: Liang
authors.initials: L
authors.lastname: Zhao
authors.forename: Caroline
authors.initials: C
authors.lastname: Williams
authors.forename: Yang
authors.initials: Y
authors.lastname: Hsia
authors.forename: Craig
authors.initials: C
authors.lastname: Vierra
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001740:Black Widow Spider; D003545:Cysteine / Q000032:analysis / Q000138:chemical synthesis*; D005349:Fibroins / Q000032:analysis / Q000138:chemical synthesis* / Q000235:genetics; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary; D047011:Silk / Q000032:analysis / Q000138:chemical synthesis* / Q000235:genetics
chemical_list: D047011:Silk; D005349:Fibroins; D003545:Cysteine