Protein Structure and the Immune System

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All proteins are made up of a series of amino acids. There are twenty different amino acids, and the type, number, and sequence of the amino acids in a given protein determine its shape and function. Proteins are essential for everyday life—they make up our organs, tissues, and muscles, and in the form of enzymes help out a vast number of different biological processes.

Protein structure and shape is an important aspect of the immune response. When it comes to antibodies, for example, protein structure is a vital aspect of function. Antibodies are an important arm of the immune system, providing us with a type of immunological memory, and the ability to react quickly to diseases our bodies have encountered before.

Protein Structure is Crucial for Antibody Function

Antibodies are proteins which are created by the immune response in response to infections. When, for example, you catch a cold, your immune system develops the ability to make antibodies which are specific to that particular cold virus. Antibodies are made by cells called B lymphocytes. These cells, which are essentially antibody factories, ingest particles—dead cells, microorganisms, and cellular debris—and then use this matter as a sort of template to create specific types of antibodies.

The way in which proteins are constructed is key to the usefulness of antibodies and immunological memory. The existence of twenty amino acids, and the fact that a protein chain can be of any length, means there is a more or less infinite number of combinations which can be created.

Another key aspect is that a B lymphocyte, once “activated” by the immune system, can create only one type of antibody. After activation, the antibodies it produces can only bind to one very short, very specific protein sequence.

Let’s say, for example, that you catch a cold. Your immune system begins to react, and your B lymphocytes are busy ingesting dead virus particles. Each B lymphocyte will create antibodies which are specific to one short amino acid sequence on one protein on the surface of the virus. This specific sequence is different for each B lymphocyte, and this diversity is just one factor which makes the whole system work as well as it does. Only a very small percentage of all B lymphocytes in the body will recognize a particular pathogen, and each recognizes a different part of the pathogen. One advantage of this diversity is that it helps somewhat to counteract the effects of pathogen mutations.

The Creation of Immunological Memory

One important fact about antibodies is that they don’t do you much good the first time you are infected with a particular type of microorganism. The antibody “factories” just can’t get going in time, and usually other arms of the immune response (which involve cells that directly kill pathogens, and are themselves dependent on protein interactions) will take care of the infection.

So what’s the use of antibodies? They’re useful the second and subsequent time that you’re infected with the same organism. The next time you catch that cold, antibody-producing B lymphocytes kick into high-gear and start producing the antibodies which can bind those crucial protein structures on the surface of the cold virus.

What happens next demonstrates just how complex and amazing the immune system is. The antibodies bind to the surface of the invading cold virus, and the unbound ends of the antibodies have special receptors which are recognized by other immune cells. Those immune cells ingest the antibodies, and destroy the attached virus particles. In most cases, your immune system will destroy the virus before it causes any symptoms.

The only downside in this scenario is that the viruses which cause colds and flu mutate extremely quickly. Your immune system will quickly and efficiently destroy a virus it has encountered previously, but when cold and flu viruses mutate, those crucial protein sequences tend to change their structure, which means your antibodies may not recognize and bind to them.