Heteroscopine (HS-1) is the main component of the venom of '' Heterometrus laoticus''. It belongs to the Scorpine toxin family. It is a polypeptide consisting of a

defensin Defensins are small cysteine-rich cationic proteins across cellular life, including vertebrate Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, ...

-like component on its N-terminal end and a putative

potassium channel Potassium channels are the most widely distributed type of ion channel found in virtually all organisms. They form potassium-selective pores that span cell membranes. Potassium channels are found in most cell types and control a wide variety of cel ...

blocking component on its C-terminal end. It has antimicrobial effect on some bacteria, but not on fungi.

Sources

Heteroscorpine (HS-1) is a component of the venom of the Thai giant scorpion '' Heterometrus laoticus''. This species is a member of the scorpion family commonly known as giant forest scorpions, indigenous to large parts of South and South-East Asia.

Chemistry

The gene coding for HS-1 consists of one intron flanked by two exons. HS-1 is a polypeptide consisting of 95 amino acids. The HS-1 protein has a large resemblance to other toxins of the Scorpine family (which is a subgroup of the Beta-KTx toxin family). The polypeptides of the Scorpine family possess two structural and functional domains: a N-terminal α-helix (which has a cytolytic and/or antimicrobial activity similar to that of insect defensins), and a C-terminal region with a CSαβ motif, which causes potassium channel-blocking activity. HS-1 is highly homologous in particular to the Scorpine toxin Panscorpine (from ''

Emperor scorpion The emperor scorpion, ''Pandinus imperator'', is a species of scorpion native to rainforests and savannas in West Africa. It is one of the largest scorpions in the world and lives for 6–8 years. Its body is black, but like other scorpions it ...

'') and Opiscorpine (from '' Opistophthalmus carinatus''), with an 80% similarity in amino acid sequence. Opiscorpine and HS-1 are both classified as scorpine-like peptides. Based on its sequence homology with other scorpine-like peptides, HS-1 is likely to be a voltage-gated potassium channel blocker. HS-1 also has antimicrobial effects on some bacterial species, i.e. ''

Bacillus subtilis ''Bacillus subtilis'', known also as the hay bacillus or grass bacillus, is a Gram-positive, catalase-positive bacterium, found in soil and the gastrointestinal tract of ruminants, humans and marine sponges. As a member of the genus ''Bacillu ...

'', ''

Klebsiella pneumoniae ''Klebsiella pneumoniae'' is a Gram-negative, non-motile, encapsulated, lactose-fermenting, facultative anaerobic, rod-shaped bacterium. It appears as a mucoid lactose fermenter on MacConkey agar. Although found in the normal flora of the mouth ...

'' and ''

Pseudomonas aeruginosa ''Pseudomonas aeruginosa'' is a common encapsulated, gram-negative, aerobic–facultatively anaerobic, rod-shaped bacterium that can cause disease in plants and animals, including humans. A species of considerable medical importance, ''P. aerugi ...

''; it has no inhibitory effects on fungi. The inhibitory effect on bacteria has no gram specificity. Scanning electron microscopy shows that HS-1 causes roughening and blebbing of bacterial cell surfaces. HS-1 contains three disulfide bridges followed by a typical Cys pattern, similar to that of invertebrate

s. Thus, HS-1 is likely to act accordingly.

Toxicity

Symptoms from envenomation in humans from the

Heterometrus ''Heterometrus'', whose members are also known by the collective vernacular name giant forest scorpions, is a genus of scorpions belonging to the family Scorpionidae. It is distributed widely across tropical and subtropical southeastern Asia, in ...

genera are reported to be of mild severity. Sting can cause redness, swelling, inflammation and pain for hours up to a few days. Injection of the purified toxin in crickets causes paralysis.

References

{{reflist Peptides Scorpion toxins