preprotoxin

Preprotoxin is a term used in toxicology and molecular biology to describe an inactive precursor molecule that, upon processing, can be converted into a potent toxin. This precursor form typically contains a signal peptide or other sequences that are cleaved off to yield the mature, active toxin. The existence of preprotoxins suggests a biological mechanism for regulating toxin production, storage, and release.

The term is derived from "protoxin," which itself is an inactive precursor of a toxin. The "pre" prefix indicates an even earlier stage of synthesis, often involving the initial translation product from the gene encoding the toxin. This initial polypeptide chain, the preprotoxin, is usually synthesized on ribosomes and targeted for secretion or insertion into cellular membranes via its signal peptide. Once inside the secretory pathway or released from the cell, this signal peptide is removed by signal peptidases, resulting in the protoxin. Further enzymatic cleavage or modification of the protoxin then liberates the active toxin.

This multi-step activation process allows for controlled delivery and action of the toxin, preventing premature or uncontrolled toxicity. Examples of biological molecules that might be considered preprotoxins are found in various organisms, including bacteria, fungi, and venomous animals, where the precise regulation of toxic activity is crucial for survival or defense. The study of preprotoxins provides insights into protein processing pathways and the evolution of toxic mechanisms.