Study for elucidating the mechanism for the specific degradation of spider silk by ultraviolet rays

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Previously, Osaki et al. showed that the silk of the Nephila clavata spider was more resistant to UV irradiation than that of the Bombyx mori silkworm. In the present study, we focused on the difference in UV resistivity between silkworm silk and spider silk from the viewpoint of molecular weight. Generally, molecular weight is determined using gel-electrophoresis method after denaturing proteins by sodium dodecyl sulfate (SDS PAGE). Here, the molecular weight of spider silk protein was determined to be 272 kDa, which is smaller than that (350 kDa) of silkworm silk using SDS PAGE.We tried to change the method for denaturing spider silk to realize the native condition. The molecular weight of native spider silk protein was determined to be about 600-700 kDa, which was much larger than that of silkworm silk. Such a large molecular weight may be ascribed to cross-linkages of protein molecules with a molecular weight of 272 kDa.