Oxotoxin

Not to be confused with oxytocin or oxyopinin.

Oxotoxins, or oxytoxins, are a group of neurotoxins present in the venom of lynx spiders belonging to the genus Oxyopes, hence the name oxytoxin. They are disulfide-rich peptides. Only two types are so far reported from two different species, the larger oxytoxin 1 (OxyTx1) from Oxyopes kitabensis, and the smaller oxytoxin 2 (OxyTx2) from Oxyopes lineatus. OxyTx1, the first known oxytoxin, was discovered in 2002. It was found to enhance the lethal efficacy of the spider venom by acting together with oxyopinins.^[1] It is composed of 69 amino acid residue, which are cross-linked by five disulfide bridges. It is a large peptide having a molecular mass of 8059.2 Da; but shows the size of 9,109.4 Da due to the presence of disulfide bridges. It is a potent insecticide, but non-toxic to mice up to 1 μg/20-g mouse. It acts synergistically with oxyopinins of the same venom to increase the insecticidal effect.

Both OxyTx1 and OxyTx2 were isolated in 2008 from O. lineatus.^[2] Both of these toxins were found to block voltage-sensitive calcium ion channels. OxyTx2 is made up of 55 amino acid residues and has a molecular mass 6175.2 Da. It is less effective in causing paralysis in Spodoptera litura larvae than Oxytx1.

Types

Oxotoxins are classified as follows:

Name	Recommended name	Size in Da	Amino acid residue	Toxicity (LD50) on S. litura
Oxytoxin 1	Omega-oxotoxin-Ol1a	8058.2	69	5.0 nmol/g
Oxytoxin 2	Omega-oxotoxin-Ol1b	6,186	55	weak activity