Glycoproteins and skin-core structure in Nephila clavipes spider silk observed by light and electron microscopy

Microscopical. imaging of natural, unstressed draglines or of untreated bul k samples showed two types or threads with diameters of either similar to 1 -2 mu m or 4-5 mu m, which could be identified as products of the minor or major ampullate glands. The threads had a circular profile in serial cross sections and are surrounded by a thin outer layer of a different material w ithin the section. Such fibrillar configurations were also found in untreat ed threads or in the same serial sections of transmission electron microsco py (TEM) samples by means of the special technique of laser scanning micros copy. In TEM slides, numerous cavities with the same circular profile were detectable, and the length of these cavities is variable from 40-300 nm. Th e threads are oriented parallel and twisted around themselves to construct a double thread. In the interface between the two single threads, bridge-li ke structures are prominent. The single untreated thread consists of cylind rical fibers with a diameter of approximately 1-1.5 mu m. Apparently more t han eight fibers are within a thread and each fiber is composed of a great number of fibrils with a diameter of about 150 nm. The surface of threads i s coated with a characteristic layer similar to 150-250 nm thick that conta ins glycoproteins. These were demonstrated for the first time by labeling w ith concanavalin A lectin-gold complex and are dependent on the diameter an d length of the thread. The same substances could also be detected inside t he single thread. The skin can be removed completely or partially by mechan ical treatment, or by washing with phosphate-buffered saline or trypsin.