CSTX (for "Cupienniussaleitoxins") is a name given to a group of closely relatedneurotoxic peptides present in the venom of thewandering spiderCupiennius salei. There are twenty types so far described for this protein group. However, some are reclassified intocupiennins group of toxin, including CSTX-3, -4, -5, and -6, because of their chemical affinity. The first thirteen were isolated and identified in 1994 by Lucia Kuhn-Nentwig, Johann Schaller, and Wolfgang Nentwig of the Zoological Institute at theUniversity of Bern,Switzerland.[1] The different types are most likely the products of splicing variant of the same gene. They are allL-typecalcium channel blockers, and also exhibitcytolytic activity by forming an alpha-helix across thecell membrane in mammalianneurons. They also inhibitvoltage-gated calcium channels in insect neurons.[2]
The best understood members of the neurotoxin group of CSTX are:
| Name | Recommended name | Size in Da | Amino acid residue | Toxicity (LD50) onDrosophilla |
|---|---|---|---|---|
| CSTX-1 | Omega-ctenitoxin-Cs1a | 8,352 | 74 | 0.35 pmol/mg |
| CSTX-8 | Toxin CSTX-8 | 7,378 | 63 | |
| CSTX-9 | U1-ctenitoxin-Cs1a | 7,529 | 68 | 10.6 pmol/mg |
| CSTX-10 | Toxin CSTX-10 | 8,110 | 69 | |
| CSTX-11 | Toxin CSTX-11 | 8,083 | 69 | |
| CSTX-12 | Toxin CSTX-12 | 7,312 | 63 | |
| CSTX-13 | U2-ctenitoxin-Cs1a | 7,359 | 63 | 16.3 nmol/g |
| CSTX-14 | Toxin CSTX-14 | 5,657 | 48 | |
| CSTX-15 | Toxin CSTX-15 | 5,612 | 48 | |
| CSTX-16 | Toxin CSTX-16 | 4,748 | 38 | |
| CSTX-17 | Toxin CSTX-17 | 4,410 | 14 | |
| CSTX-18 | Toxin CSTX-18 | 5,611 | 51 | |
| CSTX-19 | Toxin CSTX-19 | 3,748 | 35 | |
| CSTX-20 | Toxin CSTX-20 | 9,918 | 86 |
CSTX-1 is the most abundant peptide of the venom ofC. 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 fourdisulfide 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. Further, CSTX-2b also lacks arginine at position 61 compared to CSTX-1, and this reduces theneurotoxicity by 190-fold.[3] CSTX-1 exerts two different functions: as a neurotoxin it inhibits L-type calcium channels, and as a cytolytic peptide it destroys the cell membrane.[4]
