Piscivorin is a component of

snake venom Snake venom is a highly toxic saliva containing zootoxins that facilitates in the immobilization and digestion of prey. This also provides defense against threats. Snake venom is injected by unique fangs during a bite, whereas some species are a ...

secreted by the Eastern Cottonmouth (''Agkistrodon piscivorus piscivorus''). It is a member of the

cysteine-rich secretory protein Cysteine-rich secretory proteins, often abbreviated as CRISPs, are a group of glycoproteins. They are a subgroup of the CRISP, antigen 5 and Pr-1 ( CAP) protein superfamily and also contain a domain related to the ShK toxins. They are substantiall ...

(CRISP) family, which blocks voltage-dependent

calcium channels A calcium channel is an ion channel which shows selective permeability to calcium ions. It is sometimes synonymous with voltage-gated calcium channel, although there are also ligand-gated calcium channels. Comparison tables The following tables ex ...

Etymology

The name of piscivorin comes from the snake species name piscivorus, which is derived from the Latin words ''pisces'' and ''vorare'', meaning 'fish' and 'to devour' respectively.

Sources

Piscivorin is produced in the venom glands of the Eastern Cottonmouth snake (''Agkistrodon piscivorus piscivorus''), which populates the Eastern United States. Typically, crude venom from the Eastern Cottonmouth contains approximately 1.25% of piscivorin.

Biochemistry

Piscivorin belongs to the cysteine-rich secretory protein (CRISP) family, which are secreted as single-chain proteins with molecular masses between 20 and 30 kDa. They display significant amino acid sequence homology. Sixteen cysteine residues, forming 8 disulfide bonds, are strictly conserved in CRISPs. Ten of these cysteine residues are clustered into the C-terminal part of the protein. The molecular mass of piscivorin is 24.842 kDa. The nucleotide sequence of piscivorin cDNA spans 1323 bp, containing an

open reading frame In molecular biology, open reading frames (ORFs) are defined as spans of DNA sequence between the start and stop codons. Usually, this is considered within a studied region of a prokaryotic DNA sequence, where only one of the six possible readin ...

of 240 codons. Piscivorin has the following amino acid sequence.

Target and mode of action

Piscivorin reduces high potassium-evoked smooth muscle contraction, but does not inhibit

caffeine Caffeine is a central nervous system (CNS) stimulant of the methylxanthine class. It is mainly used recreationally as a cognitive enhancer, increasing alertness and attentional performance. Caffeine acts by blocking binding of adenosine t ...

-stimulated contraction of smooth muscle. Since caffeine normally causes contraction through the release of Ca²⁺ from the sarcoplasmic reticulum, this differential effect indicates that piscivorin is an

L-type calcium channel The L-type calcium channel (also known as the dihydropyridine channel, or DHP channel) is part of the high-voltage activated family of voltage-dependent calcium channel. "L" stands for long-lasting referring to the length of activation. This c ...

blocker. At a concentration of 1 μM, its effect on depolarization-induced smooth muscle contraction is weaker than of the related CRISP family toxins

ablomin Ablomin is a toxin present in the venom of the Japanese Mamushi snake, which blocks L-type voltage-gated calcium channels. Etymology The protein ablomin is a component of the venom of the Japanese Mamushi snake, ''Gloydius blomhoffii''. The ter ...

triflin Triflin is a cysteine-rich secretory protein (CRISP), which is excreted by the venom gland of the Habu snake (''Trimeresurus flavoviridis''). Triflin reduces high potassium-induced smooth muscle contraction, suggesting a blocking effect on L-type ca ...

latisemin Latisemin is a cysteine-rich secretory protein that can be isolated from the venom of the Black-banded sea krait, a sea snake indigenous to the warmer waters of the western Pacific Ocean. It is a toxin that inhibits cyclic nucleotide-gated ion ch ...

. A sequence comparison of piscivorin and other CRISP family proteins suggests that the Glu186 residue is the crucial site for the blocking of the calcium channels. Unlike some other CRISP family proteins, piscivorin does not block

cyclic nucleotide-gated channels Cycle, cycles, or cyclic may refer to: Anthropology and social sciences * Cyclic history, a theory of history * Cyclical theory, a theory of American political history associated with Arthur Schlesinger, Sr. * Social cycle, various cycles in so ...

References

{{Toxins Vertebrate toxins Ion channel toxins