Cupiennius Salei Toxin 1 (CSTX1)

CSTX-1 is the most abundant peptide of the venom of C. salei with concentration ranging from 1.4 to 3.3 mM. It is the most toxic component, and is the principle neurotoxin of the spider. It is highly basic containing four disulfide bridges, which form 'disulfide through disulfide knot', thus, structurally defines this protein as a knottin. It has two natural degradation products, namely CSTX-2a and CSTX-2b, which occur in low amount and are less toxic than the CSTX-1 itself. CSTX-2a is composed of 61 amino acid residues and has a mass of 6864 Da, while CSTX-2b is made up of 60 amino acids having a size of 6708 Da. CSTX-2a is a variation of the same gene product, and it differs from CSTX-1 only on the last 13 amino acids of the C-terminal. The 13-amino acid terminal is unusually rich in lysine (7 in number) are attributed to the higher toxicity of CSTX-1. This makes CSTX-2a seven times less toxic than CSTX-1.