| dc.description.abstract | Spider silks are desirable biomaterials characterized by high tensile strength, elasticity, and
biocompatibility. Spiders produce different types of silks for different uses, although dragline
silks have been the predominant focus of previous studies. Spider wrapping silk, made of the
aciniform protein (AcSp1), has high toughness because of its combination of high elasticity and
tensile strength. AcSp1 in Argiope trifasciata contains a 200-aa sequence motif that is repeated at
least 14 times. Here, we produced in E. coli recombinant proteins consisting of only one to four of
the 200-aa AcSp1 repeats, designated W-1 to W-4. We observed that purified W-2, W-3 and W-4 proteins
could be induced to form silk-like fibers by shear forces in a physiological buffer. The fibers
formed by W-4 were similar to 3.4 mu m in diameter and up to 10 cm long. They showed an average
tensile strength of 115 MPa, elasticity of 37%, and toughness of 34 J cm(-3). The smaller W-2
protein formed fewer fibers and required a higher protein concentration to form fibers, whereas the
smallest W-1 protein did not form silk-like fibers, indicating that a minimum of two of the 200-aa
repeats was required for fiber formation. Microscopic examinations revealed structural features
indicating an assembly of the proteins into spherical structures, fibrils, and silk-like fibers. CD
and Raman spectral analysis of protein secondary structures suggested a transition from
predominantly alpha-helical in solution to increasingly beta-sheet in fibers. | en_US |
