This family is found in Araneaea (spiders) and family members are venomus peptides with 4 disulfide bonds. Cystine knot toxins (CKTs) are small, compact molecules cross-linked by three to five disulfide bonds and are often the key contributors to the activity and potency of the venom [1]. While these disulfide-rich peptides can adopt a number of different structural motifs, three of the most observed structural scaffold motifs are the inhibitor cystine knot (ICK) and the disulfide-directed beta-hairpin (DDH) and Kunitz motif. These venomus peptides mainly act on membrane proteins in electro-excitable cell membranes by modulating voltage-activated sodium (NaV), calcium (CaV), and potassium (KV) channels, acid-sensing ion channels (ASICs), transient receptor potential (TRP) channels, and mechanosensitive channels (MSCs) [2].

1: Molecular diversity and evolution of cystine knot toxins of the tarantula Chilobrachys jingzhao. Chen J, Deng M, He Q, Meng E, Jiang L, Liao Z, Rong M, Liang S; Cell Mol Life Sci. 2008;65:2431-2444. PMID:18581053

2: Spider-venom peptides as bioinsecticides. Windley MJ, Herzig V, Dziemborowicz SA, Hardy MC, King GF, Nicholson GM; Toxins (Basel). 2012;4:191-227. PMID:22741062