Affitins are artificial protein

Protein

Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

s with the ability to selectively bind antigen

Antigen

An antigen is a foreign molecule that, when introduced into the body, triggers the production of an antibody by the immune system. The immune system will then kill or neutralize the antigen that is recognized as a foreign and potentially harmful invader. These invaders can be molecules such as...

s. They are structurally derived from the DNA

DNA

Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...

 binding protein Sac7d, found in Sulfolobus

Sulfolobus

Sulfolobus is a genus of microorganism in the family Sulfolobaceae. It belongs to the archea domain.Sulfolobus species grow in volcanic springs with optimal growth occurring at pH 2-3 and temperatures of 75-80 °C, making them acidophiles and thermophiles respectively...

 acidocaldarius, a microorganism belonging to the archaea

Archaea

The Archaea are a group of single-celled microorganisms. A single individual or species from this domain is called an archaeon...

 domain. By randomizing the amino acid

Amino acid

Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...

s on the binding surface of Sac7d and subjecting the resulting protein library to rounds of ribosome display

Ribosome display

Ribosome display is a technique used to perform in vitro protein evolution to create proteins that can bind to a desired ligand. The process results in translated proteins that are associated with their mRNA progenitor which is used, as a complex, to bind to an immobilized ligand in a selection step...

, the affinity can be directed towards various proteins. Affitins are antibody mimetic

Antibody mimetic

Antibody mimetics are organic compounds that, like antibodies, can specifically bind antigens, but that are not structurally related to antibodies. They are usually artificial peptides or proteins with a molar mass of about 3 to 20 kDa...

s and are being developed as an alternative to antibodies as tools in biotechnology

Biotechnology

Biotechnology is a field of applied biology that involves the use of living organisms and bioprocesses in engineering, technology, medicine and other fields requiring bioproducts. Biotechnology also utilizes these products for manufacturing purpose...

. They have also been used as specific inhibitors for various enzymes.

Properties

Affitins consist of 66 amino acids and have a molecular mass

Molecular mass

The molecular mass of a substance is the mass of one molecule of that substance, in unified atomic mass unit u...

 of about 7 kDa

KDA

KDA may refer to:* Karachi Development Authority* Kongsberg Defence & Aerospace* Kotelawala Defence Academy* Kramer Design Associates* Lithium diisopropylamide, KDA is the potassium analogue of lithium diisopropylamideOr kDa may refer to:...

, small compared to antibodies with some 130–150 kDa. Being obtained from a thermophile

Thermophile

A thermophile is an organism — a type of extremophile — that thrives at relatively high temperatures, between 45 and 122  °C . Many thermophiles are archaea...

organism, they are unusually heat resistant proteins. Unlike antibodies, novel affitins are produced in vitro, and therefore can be generated on a shorter timescale. Due to their small size and high solubility, they can be easily produced in large amounts using bacterial expression systems.