TOUGH TENDONS - MUSSEL BYSSUS HAS COLLAGEN WITH SILK-LIKE DOMAINS

The primary structure of the alpha-chain of preCol-D (molecular mass = 80 kDa), a tanned collagenous protein predominating in the distal por tion of the byssal threads of the mussel Mytilus edulis, was deduced f rom cDNA to encode an unprecedented natural block copolymer with three major domain types: a central collagen domain flanked by fibroin-like domains and followed by histidine-rich termini, The fibroin-like doma ins have sequence motifs that strongly resemble the crystalline polyal anine-rich and amorphous glycine-rich regions of spider dragline silk fibroins. The terminal regions resemble the histidine-rich domains of a variety of metal-binding proteins. The silk domains may toughen the collagen by increasing its strength and extensibility. PreCol-D expres sion is limited to the mussel foot, which contains a longitudinal grad ient of preCol-D mRNA. This gradient increases linearly in the proxima l to distal direction and reaches a maximum just before the distal dep ression of the foot.