How many peptides are there

This article is a U. Government work and is in the public domain in the USA. Abstract Over the last 5 years proteogenomics using mass spectroscopy to identify proteins predicted from genomic sequences has emerged as a promising approach to the high-throughput identification of protein N-termini, which remains a problem in genome annotation. He wanted to see whether studying how eggshells form could help inform research on teeth and bones. But he soon realized that the eggshell had even more potential than being a simple model system for calcification.

In particular, Hincke and his colleagues have homed in on eggshell biopeptides that fight microbes. While all animals have proteins called beta-defensins that help fight disease, for instance, Hincke has unearthed a new beta-defensin that is unique to eggs and may be able to treat bacterial infections that have classically resisted antibiotics. The finding is an example of why it is so important to isolate and characterize biopeptides from new sources, Hincke says.

Hincke has now isolated some from chicken blood, and others have pinpointed them in the breakdown products of cow and goat milk, beef, and whey. Each works a different way: some bust a microbe's outer membrane, whereas others interfere with the microbe's production of DNA or proteins.

Some work against nearly all microbes, while others are more specific-a peptide from goat milk cheese, for instance, has been found to improve the symptoms of people infected with Helicobacter pylori.

There are likely more antimicrobial peptides that have yet to be discovered, Hincke points out. Because many biopeptides are produced when food is broken down in the gut, it is not surprising that many of these mini-proteins have an effect on satiety, appetite, or how the body digests food.

In an age of obesity, heart disease, and diabetes epidemics, it is obvious why scientists would be actively researching these effects of biopeptides.

Often, research starts because scientists know that a food source is particularly good at making people feel full-or at lowering blood pressure or cholesterol. Then, researchers try to pin down what proteins or peptides are causing this effect. For Hara, it began with soybeans. Other researchers have found that fish and seafood are a plentiful source of bioactive peptides that modulate appetite, blood pressure, blood sugar, or cholesterol.

Toshiro Matsui, a professor of bioscience at Kyushu University in Fukuoka, Japan, has isolated tiny peptides-some only two amino acids long-from soybeans, egg whites, and teas-that apparently help prevent high blood pressure and clogged arteries.

The peptides he has found, he believes, affect levels of calcium inside cells, which is key to how they signal. But other peptides exhibit similar effects by blocking a protein called angiotensin-converting-enzyme ACE , causing blood vessels to relax. Matsui is still characterizing all the effects of the biologically active amino acid pairs that he has identified.

To better understand these roles, he has developed a method of labeling peptides to track their movement through the body. Both Hara and Matsui say that scientists someday may be able to integrate the peptides they find into pills or even food itself to help prevent obesity and diabetes. But, as is the story for many newly discovered biopeptides, more work is needed to characterize the peptides before that can happen. If you read the front of cosmetic containers-everything from anti-aging facial lotion to shampoo-you might think there is one area where biopeptides are already making a big splash in the commercial world.

You will see "peptide-infused eye cream," "peptide lip therapy," and "peptide cleansing gel" at the beauty counter. But don't jump to conclusions just yet. In fact, he points out, if cosmetics did have bioactive peptides in them, they would no longer be just a cosmetic; they would have to be regulated by the US Food and Drug Administration FDA as a drug. That is because a cream or cleanser that interacts with the skins' metabolism-which a peptide would need to do to be dubbed "bioactive"-falls under the FDA's jurisdiction.

But Romanowski does admit the claims-in some cases-aren't just pulled out of nowhere. There are a number of biologically active peptides that research has shown might have anti-aging or wrinkle-removing properties.

They are just not likely to be in over-the-counter creams any time soon. Peptides advertised in cosmetics-both those that fail to provide their alleged function and those found in drugs that do-generally fall into one of a few categories.

Neurotransmitter peptides, such as the botulinum toxin used in Botox TM , affect the function of nerve cells and can reduce wrinkles by relaxing muscles in the face. But the definition, and the way scientists use each term, is a little loose.

As a general rule, a peptide contains two or more amino acids. And just to make it a little more complicated, you will often hear scientists refer to polypeptides — a chain of 10 or more amino acids. But most peptides found in the human body are much shorter than that — chains of around 20 amino acids. As with the peptide and the protein, the cyclotide is also comprised of a string of amino acids, but unlike the others, the ends of a cyclotide are joined together to form a circle.

Haemoglobin, found in your red blood cells and essential for carrying oxygen, is such a protein. Biochemists are excited by the possibilities presented by peptides and proteins as pharmaceuticals because they so often mimic exactly the behaviour of a natural ligand — the substance that interacts with the receptor on an enzyme or cell to cause a biological process. This gives peptide drugs the potential to be more precisely targeted, with fewer side effects than small-molecule drugs.

Within the body, there are lot of different hormones that react with cells and trigger different biological processes. Often these are peptides, either cyclic versions or straight, linear ones. There are also manufacturing considerations that make peptides attractive — their length allows them to be chemically synthesised, as opposed to proteins that are generally expressed in yeast or mammalian cells.

The most promising application of proteins is as antibodies , which are themselves a form of protein. Particularly in anti-cancer applications, there are a lot of antibodies either in the clinic or under development. Two well-known examples are Herceptin trastuzumab for breast cancer, and Humira adalimumab for rheumatoid arthritis and other autoimmune diseases.

In the case of antibodies, protein-based drugs use the same strategy as the body does to target things.