Small disulfide-rich protein characterized by a special 'disulfide through disulfide knot'. This knot is obtained when one disulfide bridge crosses the macrocycle formed by two other disulfides and the interconnecting backbone (disulfide III-VI goes through disulfides I-IV and II-V). The knottin structure is found in some plant protease inhibitors, cyclotides, toxins from cone snails, spiders, insects, horseshoe crabs and scorpions, gurmarin-like peptides, agouti-related proteins, and some antimicrobial peptides.
