Mipartoxin-I is a
neurotoxin
Neurotoxins are toxins that are destructive to nerve tissue (causing neurotoxicity). Neurotoxins are an extensive class of exogenous chemical neurological insultsSpencer 2000 that can adversely affect function in both developing and mature ner ...
produced by ''
Micrurus mipartitus
''Micrurus mipartitus'' (red-tailed coral snake or many-banded coral snake) is a species of coral snake in the family Elapidae. It is found in South and Central America. The redtail coral snake is common in agricultural areas in Colombia. Its h ...
'', a venomous
coral snake
Coral snakes are a large group of elapid snakes that can be divided into two distinct groups, the Old World coral snakes and New World coral snakes. There are 16 species of Old World coral snakes, in three genera (''Calliophis'', '' Hemibungarus' ...
distributed in Central and South America. This toxin causes a
neuromuscular blockade
Neuromuscular-blocking drugs block neuromuscular transmission at the neuromuscular junction, causing paralysis of the affected skeletal muscles. This is accomplished via their action on the post-synaptic acetylcholine (Nm) receptors.
In clin ...
by blocking the
nicotinic acetylcholine receptor. It is the most abundant component in the
venom
Venom or zootoxin is a type of toxin produced by an animal that is actively delivered through a wound by means of a bite, sting, or similar action. The toxin is delivered through a specially evolved ''venom apparatus'', such as fangs or a sti ...
.
Sources
The toxin is produced by the ''Micrurus mipartitus'', also known as the ‘redtail coral snake’, ‘''rabo de ají''’, or ‘''gargantilla''’.
The snake populates Nicaragua, Costa Rica, isthmus of Panama, Ecuador, Colombia, Venezuela and Brazil.
Chemistry
Structure and family
Mipartoxin-I is a short-chain, type-I,
α-neurotoxin composed of 60 amino acids with a molecular mass of 7030 Da.
It is a member of the
three finger toxin (3FTx) superfamily, and it contains the characteristic eight
cysteine
Cysteine (symbol Cys or C; ) is a semiessential proteinogenic amino acid with the formula . The thiol side chain in cysteine often participates in enzymatic reactions as a nucleophile.
When present as a deprotonated catalytic residue, sometime ...
s of this superfamily.
Homology
CTX A5, a
cardiotoxin
Cardiotoxicity is the occurrence of heart dysfunction as electric or muscle damage, resulting in heart toxicity. The heart becomes weaker and is not as efficient in pumping blood. Cardiotoxicity may be caused by chemotherapy (a usual example is th ...
from the cobra
''Naja'' ''atra'', shows similarities with mipartoxin-I in the predicted core region and in amino acid sequence identity (38%). However, there are some slight differences in loop 1 and 2, and major differences in loop 3.
Mipartoxin-I generally shows relatively low sequence similarity with other 3FTx family members.
Target
Mipartoxin-I is proposed to bind antagonistically to the
nicotinic acetylcholine receptors and consequently inhibit the activity of this receptor without damaging the muscle fibres.
The toxin blocks the muscle contractions without interfering with presynaptic acetylcholine release, indicating that it acts post-synaptically.
Toxicity
Envenoming mice with Mipartoxin-I causes bilateral
ptosis and progressive respiratory paralysis. Following a decrease in activity and respiratory paralysis, mice die a few hours after envenoming. The
LD50 of mipartoxin-I is 0.06 μg/g body weight.
Treatment
Currently, no specific
antivenom is available in most of its important geographic field (Central America). The scarcity of an antivenom is complicated by insufficient cross-protection by antivenoms that are more accessible in this geographic area. However, the similarity in amino acid sequence of related toxins of two South American coral snakes were high (
''M.'' ''frontalis'' 70% and
''M.'' ''altirostris'' 68%). This indicates a possible cross-protection of these two antivenoms for mipartoxin-I.
References
{{Reflist
Ion channel toxins
Neurotoxins
Vertebrate toxins