| Primary Identifier | IPR044061 | Type | Domain |
| Short Name | OXYTX_ICK |
| description | Spiders are widely acknowledged to produce potent and selective toxins. In addition to the conventional neurotoxins and cytotoxins, venom of lynx spiders (genus Oxyopes) was found to contain two-domain modular toxins named spiderines: OspTx1a, 1b, 2a and 2b [, , ]. Spiderines consist of two distinct modules separated by a short linker. The N-terminal part (~40 residues) contains no cysteine residues, is highly cationic, forms amphipathic alpha- helical structures in a membrane-mimicking environment, and shows potent cytolytic effects on cells of various origins. The short linker resembles closely the processing quadruplet motif (PQM), which is known to indicate the processing cleavage site in precursors of spider toxins and separate the prosequence from the mature chain. The C-terminal part (~60 residues) is a disulfide rich domain reticulated by five S-S bridges that is homologous to one-domain oxytoxins (OxyTx1 and OxyTx2) from Oxypes species. Oxytoxins are disulphide-rich polypeptides that contain five disulfide bridges and block L-, N- and P/Q-type voltage-sensitive calcium ion channels (VSCCs) []. The core of the oxytoxin-like domain is the inhibitor cystine knot (ICK) or knottin motif. The domain is stabilised by five disulfides and 13 hydrogen bonds. Two antiparallel β-strands form a short β-sheet, and there are two β-turns in the N-terminal part of of the domain. C1-C5, C2-C6, and C4-C9 disulfides contribute to the ICK motif, whereas C7-C8 stabilises the extended loop of the β-hairpin and C3-C10 staples the lengthy C-terminal of the domain to its core [].This entry represents the oxytoxin-type ICK domain. |
