243 Investigating the Molecular Structure and Conformation of Spider Silk Proteins with Solid-State NMR

Thursday, November 5, 2009: 11:40 AM
Hereford (Camino Real Hotel)
Janelle E. Jenkins , Department of Chemistry & Biochemistry, Arizona State University, Tempe, AZ
Gregory P. Holland , Department of Chemistry & Biochemistry, Arizona State University, Tempe, AZ
Jeffery L. Yarger , Department of Chemistry & Biochemistry, Arizona State University, Tempe, AZ
Spider silk is nature's super biopolymer with unsurpassed mechanical properties combining a strength comparable to Kevlar and an extensibility that surpasses nylon. Dragline silk is made of two proteins: Major ampullate spidroin 1 and 2 (MaSp1 and MaSp2) and has been described as a co-biopolymer. A better understanding of the molecular conformation of the proteins and how this correlates to the mechanical properties of the silk is needed. To date, most of the structural characterization of spider silk has been on the Nephila species that has a MaSp1:MaSp2 ratio of 80:20. MaSp2 has a high proline content that has been correlated to a number of interesting properties such as elasticity and supercontraction is spider silks. Although β-spirals and turn-like secondary structures have been proposed for the proline-rich GPGXX motif in MaSp2, experimental evidence is lacking to prove these structural arrangements. The Argiopes species produces silk that contains a larger percentage of MaSp2 compared to Nephila, with a ratio of 40:60 MaSp1 to MaSp2. Thus, both Nephila and Argiopes silks are used to characterize the two proteins, MaSp1 and MaSp2, respectively. NMR structural characterization of the silk fibers and the protein producing glands has been performed using solid-state and High Resolution Magic Angle Spinning (HR-MAS) NMR spectroscopy, respectively. In the fiber, a combination of hetero-nuclear and homo-nuclear experiments utilizing dipolar-transfer and J-transfer were used for assignment of resonances and conformational characterization of the proteins. For example, the utility of through-bond 13C-13C solid-state refocused INADEQUATE experiments will be highlighted.