What is the primary protein in spider silk?

The primary proteins in spider silk are called spidroins. They form a family of specialized structural proteins that spiders tailor for different types of silk, including draglines, capture threads, egg sacs, and prey-wrapping fibers.

The best-studied examples are major ampullate spidroins, commonly abbreviated MaSp1 and MaSp2. These proteins are especially important in dragline silk, the strong thread used for web frameworks, safety lines, and escape lines. Their amino-acid sequences contain repetitive regions rich in glycine and alanine, which help create a combination of strength and flexibility.

Fibroin is a common mix-up because it is the principal protein in silkworm silk. Keratin and collagen are also structural proteins, but they are associated mainly with tissues such as hair, nails, skin, bones, and connective tissue rather than spider silk.

Spiders produce several chemically distinct silks rather than one universal thread. Different silk glands make different spidroin-related proteins, and the spider’s spinning duct helps transform a concentrated protein solution into a solid fiber. This molecular organization gives some spider silks remarkable toughness without making them rigid.