Peptides are short chains of amino acids. These are the same building blocks that make up all proteins. The difference is that peptides are much shorter, never over 100 amino acids long. Historically, peptides had a boom in the early 60’s, when chemical peptide synthesis was invented. However, they lost their role in the late 70’s, when the spotlight began shifting towards nucleic acids such as DNA. Only recently have peptides been “rediscovered” as a trend for scientific investigations, as more questions arise from the studies of genomics. Many peptides occur naturally in living organisms, all encoded in our DNA sequences. Among these are various enzymes, such as those that break down foods in our stomach. Several hormones are also peptides, including the precursor for insulin, which is one of the hormones in charge of maintaining healthy levels of sugars in the blood. Peptides can also be found in the brain, acting as molecules that carry messages from cell to cell. These messengers, called neurotransmitters, are responsible for complex responses commanded by the nervous system. For examples, endorphins released during exercise are also peptides.
As time passed and molecular biology progressed, peptides started appearing in a wide diversity of roles in organisms ranging throughout all the kingdoms of life. Bacteria were found to produce peptides that act as toxins against the target host. Plants and fungus in turn, use peptides as antibiotic molecules, and these same peptide have been synthesized and those interested are able to buy peptides from reliable sources . The immune system was found to break down pathogen proteins into peptides and use them as to identify infectious agents. Likewise, peptides are also used as signals within an organism or a cell itself. Peptides seem to be involved in several conditions; including neurodegenerative disorders such Alzheimer’s Disease and prion illnesses such as Bovine Spongiform Encephalopathy (also known as Mad Cow disease). The list goes on and on.
Why have we just now started focusing our attention back onto peptides? The answer is simple. We could not see them in the genome. During the first years of this century, when large efforts were being put into deciphering the human genome, scientist ran into a brick wall. There were more proteins than genes. How could this be? All proteins and peptides are produced from mRNA, which a molecule that acts as a template of our DNA. Therefore one gene meant one protein. Of course some proteins or peptides could me modified after being created, like the case of insulin, which needs to be cut by an enzyme in a certain location to become active, but in general the idea stood. Then came a few exceptions. In certain cases this mRNA could be modified before being translated into a protein. This process was dubbed splicing. If a single mRNA was spliced in different ways, then one gene could produce a wide array of proteins or peptides. Further research concluded that this was more of a norm than an exception. Our entire immune system, for instance, is based on this principle.
So now suddenly, the genome became rich in possible peptides that we could not see before. Scientist sought out to find peptides in new places. And they found them everywhere. Nowadays, production of peptides is much easier than before using classic cloning systems. Sequences that code a peptide are introduced into bacteria and then the bacteria are allowed to reproduce. These genetically modified bacteria produce large amounts of the peptide of interest, which is then extracted from this culture. This has given molecular biology a powerful tool that takes advantage of the universal presence of peptides.
Leading biotechnology companies are using peptides for research. Examples include the search for natural pesticides in the food industry. Given the trend for more natural, chemical free products, natural peptides with antifungal or antibacterial properties are being investigated to replace current compounds used in agriculture and fish farming. The search for new antibiotics to combat antibiotic resistance may lie in modification of naturally occurring antibiotic peptides. The vaccine industry is also taking advantage of peptides. Since peptides from pathogens are presented to the immune system as epitopes (small 3D peptide structure motifs) to trigger a response, it is quite easy to synthesize a wide array of different peptides to act as test molecules to discover the exact sequences that our body recognizes. Thus, vaccinations will become safer, as we no longer need to use complete microorganisms in vaccines. We are also able to target several epitopes at once, thus reducing the risk of resistance.
Research and biotech now thrive on the potential of peptides. Novel applications for peptides are under research in laboratories all over the world. Bioinformaticians work at predicting novel peptides each day. And the science of peptides is just starting to take off.