Spider silk consists of fiber-forming proteins, stored by the spider in a specialized gland. When the spider needs silk, for instance to build a web, it extrudes the silk proteins through a long duct in which they are exposed to specific mechanical and chemical influences and assembled to form silk. Spider silk proteins, like all proteins, consist of 20 elementary building blocks known as amino acids. The number and sequence of these amino acids determines the properties of individual proteins. For example, if hydrophobic amino acids such as leucine are located in the center of a protein, the result is considerable structural stability. Thus you might expect the extremely strong spider silk to contain a lot of leucine. Much to their surprise, however, scientists from the universities of Mainz and Würzburg discovered that another building block, methionine, is highly abundant in some spider silk proteins.

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