The most important reason why snake venom is such a goldmine for the pharmaceutical industry and drug development, is its origin and evolution. It is wrong to assume that all venom components are derived from saliva proteins. Actually, they are mainly mutated body proteins. Those body proteins often play a crucial role in physiological processes such as the regulation of blood pressure, conduction of nerve impulses, immune responses (the complement system), regulation of cardiac rhythm, and others.
These mutant proteins are being generated by gene duplication followed by gene recruitment events. Every cell (except for gametes and some non-nucleated cells) contains a complete copy of the genome. This genome contains thousands of genes. According to ensembl the human genome has around 20,000 protein coding genes. It is not unreasonable to assume that snakes have a similar number, although there is currently no genome build available for any snake. Not all these genes are expressed in every cell. The set of genes that are expressed or (“switched on” or transcribed) are different for each cell type, and also vary at different life stages. For example, in the heart a different set of genes is expressed than in the brain. These expressed genes produce RNA, which is involved in the formation of proteins. Every different RNA molecule leads to a different kind of protein. The transcriptional profile of venom glands of snakes is a very nice example of what evolution can do.
During evolution, gene duplication followed by gene recruitment may take place in the venom gland. At such times, a gene which is normally only expressed in the heart muscle, for example, can suddenly become switched on in the venom gland. Suppose that the resulting protein regulates the heart beat of the snake, and that it leads to a heart attack in the prey when it is injected. This would be evolutionary beneficial for the snake, since the new component in the venom causes rapid immobilization of the prey item. Natural selection will likely fix this gene in the venom of a population of snakes. Subsequently, generations of evolution and mutations may lead to the gene, and the resulting protein, getting more and more potent. ‘Potency’ is an important concept in venom research because it referes to the quantity of a substance that is needed to exert a particular effect. And so, more potent molecules only need to be present in smaller quantities to cause cardiac arrest in the prey.
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