CSTX (for "Cupiennius saleitoxins") is a name given to a group of closely related neurotoxic peptides present in the venom of the wandering spiderCupiennius salei. There are twenty types so far described for this protein group. However, some are reclassified into cupiennins 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 the University of Bern, Switzerland.[1] The different types are most likely the products of splicing variant of the same gene. They are all L-typecalcium channel blockers, and also exhibit cytolytic activity by forming an alpha-helix across the cell membrane in mammalian neurons. They also inhibit voltage-gated calcium channels in insect neurons.[2]
Types
The best understood members of the neurotoxin group of CSTX are:
Name
Recommended name
Size in Da
Amino acid residue
Toxicity (LD50) on Drosophilla
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
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. Further, CSTX-2b also lacks arginine at position 61 compared to CSTX-1, and this reduces the neurotoxicity 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]
References
^Kuhn-Nentwig L, Schaller J, Nentwig W (1994). "Purification of toxic peptides and the amino acid sequence of CSTX-1 from the multicomponent venom of Cupiennius salei (Araneae:Ctenidae)". Toxicon. 32 (3): 287–302. Bibcode:1994Txcn...32..287K. doi:10.1016/0041-0101(94)90082-5. PMID8016851.
^Kuhn-Nentwig L, Schaller J, Kämpfer U, Imboden H, Malli H, Nentwig W (2000). "A lysine rich C-terminal tail is directly involved in the toxicity of CSTX-1, a neurotoxic peptide from the venom of the spider Cupiennius salei". Archives of Insect Biochemistry and Physiology. 44 (3): 101–111. doi:10.1002/1520-6327(200007)44:3<101::AID-ARCH1>3.0.CO;2-S. PMID10897091.
