STRUCTURAL STUDIES OF SPIDER-SILK FIBERS:

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. pider silk is a bio-polymer comprised of long, helical, fibrous structure. Spider dragline silks have unsurpassed mechanical strength, a combination of very high elasticity and tensile strength [1,2]. A knowledge of the micro-structure of the silk fibers is crucial in understanding their unique mechanical properties. This knowledge would help in the design of new smart bio-materials for numerous applications ranging from airbags to sensors to micro-sutures to artificial ligaments and tendons to drug delivery coatings [3]. Typical spider webs are constructed from several different silks, each of which is produced in a different gland [2]. Due to their large size and ease of study, major ampullate (MA) glands have received the most attention. Previous diffraction studies have been done on dragline silk indicate that the MA silk is a semicrystalline biopolymer composed of crystalline domains consisting of ¿-(L-polyalanine) sheets embedded in a glycine rich amorphous matrix [4-6]. Comparatively little is known about other silks, eg, the silk of the minor ampullate (MI) glands, which often accompanies MA silk. Supercontraction: Addition of water to Nephila Clavipes MA silk or dragline silk results in fiber contraction to 50% its initial length, and significant changes to the mechanical properties of the silk [7]. This phenomenon has been termed supercontraction. Current understanding from a few studies on the MA silk indicate that the crystalline ¿-sheet regions in the wet silk are more or less intact [8-9].To the best of our knowledge, there is no systematic diffraction studies on the dry and wet-supercontracted fiber on both the MA and the MI silks.Fiber diffraction is the only practical method of structure determination at the molecular level for these assemblies [10, 11].We propose to carry out fiber diffraction experiments on both major and minor ampullate silks extracted from Nephila clavipes on the dry and supercontratcted-wet silks.