INTELLECTUAL MERIT: Spider silk is among the most interesting of all the naturally occurring fibers. A spider may produce up to six different silks which display a wide range of strength and extensibility. In some cases the strength and extensibility significantly exceed what has been observed in man made fibers. Some dragline silks exhibit the phenomenon of supercontraction wherein they contract by as much 55% in length upon exposure to water, leading to an increase in extensibility and reduction in strength. The origin of different behaviors in different silks is thought to relate to the primary amino acid sequence and to the secondary structure of the peptide chain, which has yet to be fully understood. The proposal outlines a schedule of research, based largely on solid state nuclear magnetic resonance spectroscopy (NMR) and neutron and X-ray scattering, designed to provide a major extension of our knowledge of the molecular structure and dynamics in the disordered region in spider silk fibers. The objectives are as follows: (1) Develop NMR spectroscopic techniques to better elucidate the short-range order, intermediate range order and/or secondary structure in amorphous or semi-crystalline biopolymers, such as spider silk fibers. (2) Better elucidate the role water plays in the (i) solvation, (ii) plastizing, and (iii) as an intercalant molecule in spider silk fibers and to determine both dynamic and structural changes brought about by hydration. (3) Provide a complete secondary structural analysis of the amorphous region in spider silk fibers using multidimensional, multinuclear NMR spectroscopy. (4) Use X-ray and neutron diffraction in collaboration with scientists at the Argonne National Laboratory to further elucidate the short and intermediate range order in spider silk fibers. (5) Correlate information regarding secondary structure with known primary amino acid sequences in order to devise a fundamental understanding of how these repetitive motifs relate to spider silk?s impressive mechanical properties. (6) Use the group's expertise in multi-instrument characterization of amorphous materials to further elucidate thermal and physical properties of spider silk materials.
BROADER IMPACTS: These studies offer a new window into the relationship of structure and mechanical properties of a fascinating class of natural biological fibers. Understanding of these substances can lead to design of better synthetic polymers for a variety of important applications. Students involved in the project will be trained for scientific careers in biomaterials science, physical chemistry, and chemical physics and will have an opportunity to become familiar with the capabilities of a major national laboratory. The PI participates in several educational and outreach activities. He has teamed with the Center for Research on Education in Science, Mathematics, Engineering and Technology (CRESMET) to become a research lab partner for the inaugural 2007 Math and Science Teaching Fellows program at Arizona State University. This program brings high school and junior high teachers into the research labs for the summer for immersion in active research and the development of activities for articulating research into their K-12 classrooms. This program is funded jointly by the National Science Foundation and Science Foundation Arizona, and continues throughout the school year with in-school activities, including regular communication with the PI and research group members at the university and at the school site. An emphasis has been placed on involving underrepresented minorities in both research and educational outreach projects. Specifically, several school districts with large populations of Hispanic and Native American students have been targeted for the K-12 outreach activities described above.
The ability to duplicate spider silk properties in man-made protein based materials is the key to using these high-performance biopolymers in ‘real-world’ applications. A first step in this process is giving engineers the molecular level detailed information about the structure and dynamics in the natural material, in order to reproduce this in recombinant or synthetic constructs. Our research project developed new understandings into the structural and dynamic changes involved in supercontraction and extraction of natural spider silk. The NSF funded research project involved a student research team consisting of graduate, undergraduate and high-school students. The research team was exposed to scientific research and instrumentation at both Arizona State University and Argonne National Laboratory. Our research group also participate in NSF sponsored K-12 teacher summer research programs and provided demonstrations of spider silk research to local area K-12 schools. Specific emphasis was placed on outreach to underrepresented hispanic and native american schools and neighborhoods. Spiders produce a variety of silks with mechanical properties that can outperform other natural and synthetic fibers. A complete picture of the molecular underpinnings responsible for these high-performance materials remains unsolved, even for the most studied dragline silk fibers. The quintessential aspect that is often overlooked in silk is that the majority of the materials are disordered or amorphous. Understanding the molecular structure and dynamics in the amorphous region is critical to the ultimate goal of producing a protein-based material with properties similar to spider draglines. Our research group at Arizona State University under the direction of Prof. Jeff Yarger (PI) and Prof. Greg Holland (Co-PI) developed solid state NMR methods and XRD fiber diffraction methods to elucidate the molecular structure and dynamical behavior of Nephila Clavipes, Argiope Aurantia and Latrodectus Hesperus spider silks. We discovered the molecular underpinnings for supercontraction, when unconstrained silk is exposed to water, and helped to further establish relationships between structure and mechanical function in natural silks.
