| Spider silks have been the subject of interest for centuries because of their intriguing properties. An orb web, the typical spider web, is constructed of several different silk fibers, each synthesized by a different gland. The best studied spider silk is dragline (major ampullate) silk from Nephila clavipes. Minor ampullate silk is a related but less well characterized fiber. Both major and minor ampullate silks have high tensile strengths. Minor ampullate silk irreversibly deforms when stretched, but major ampullate silk is elastic. The structure/function relationship of dragline silk proteins can explain the strength and elasticity of these fibers. The focus of this work is to develop a model for the minor ampullate silk proteins to explain why these fibers are strong and inelastic.; Major and minor ampullate silks are composed virtually entirely of protein. The partial primary structures of the two major ampullate silk proteins (MaSp 1 and MaSp 2) are known. Structural analyses indicate regions of crystallinity associated with the {dollar}beta{dollar}-sheet structures responsible for the extraordinary tensile strength of the fiber. The predicted structure of MaSp 2 is that of an elastin-like protein, which could exist in a stacked {dollar}beta{dollar}-turn or coil structure, which may be essential for fiber elasticity.; Results of this work have provided a much better understanding of the structure and function of spider silk proteins. We now know that minor ampullate silk is composed of two proteins, MiSp 1 and 2, whose transcripts are 9.5 and 7.5 kb, respectively. More sequence data was generated for minor ampullate silk proteins than for any other spider silk. As a result, this study revealed the hierarchy of minor ampullate silk protein organization. {dollar}beta{dollar}-sheet-forming glycine-alanine and possibly helical glycine-rich domains of the two proteins. A large amount of {dollar}beta{dollar}-sheets are formed by the interaction of many MiSp 1 and 2 proteins and account for the tremendous tensile strength of the fiber. The absence of an elastin-like protein is the basis for the inelasticity in minor ampullate silk. We now have a better understanding of the synthesis, structure and function of this class of structural proteins. |
