Antibody mimetics are organic compounds that, like antibodies, can specifically bind antigens, but that are not structurally related to antibodies. They are usually artificial peptide

Peptide

Peptides are short polymers of amino acid monomers linked by peptide bonds. They are distinguished from proteins on the basis of size, typically containing less than 50 monomer units. The shortest peptides are dipeptides, consisting of two amino acids joined by a single peptide bond...

s or 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 a molar mass

Molar mass

Molar mass, symbol M, is a physical property of a given substance , namely its mass per amount of substance. The base SI unit for mass is the kilogram and that for amount of substance is the mole. Thus, the derived unit for molar mass is kg/mol...

 of about 3 to 20 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:...

. Nucleic acid

Nucleic acid

Nucleic acids are biological molecules essential for life, and include DNA and RNA . Together with proteins, nucleic acids make up the most important macromolecules; each is found in abundance in all living things, where they function in encoding, transmitting and expressing genetic information...

s and small molecule

Small molecule

In the fields of pharmacology and biochemistry, a small molecule is a low molecular weight organic compound which is by definition not a polymer...

s are sometimes considered antibody mimetics as well, but not artificial antibodies, antibody fragments and fusion protein

Fusion protein

Fusion proteins or chimeric proteins are proteins created through the joining of two or more genes which originally coded for separate proteins. Translation of this fusion gene results in a single polypeptide with functional properties derived from each of the original proteins...

s composed from these. Some types have an antibody-like beta-sheet structure. Common advantages over antibodies are better solubility

Solubility

Solubility is the property of a solid, liquid, or gaseous chemical substance called solute to dissolve in a solid, liquid, or gaseous solvent to form a homogeneous solution of the solute in the solvent. The solubility of a substance fundamentally depends on the used solvent as well as on...

, tissue penetration, stability towards heat and enzymes, and comparatively low production costs. Antibody mimetics are being developed as therapeutic and diagnostic

Medical diagnosis

Medical diagnosis refers both to the process of attempting to determine or identify a possible disease or disorder , and to the opinion reached by this process...

 agents.

Examples

Antibody mimetic	Scaffold	Molar mass	Example drug
Affibody molecules	Z domain of Protein A Protein A Protein A is a 40-60 kDa MSCRAMM surface protein originally found in the cell wall of the bacterium Staphylococcus aureus. It is encoded by the spa gene and its regulation is controlled by DNA topology, cellular osmolarity, and a two-component system called ArlS-ArlR. It has found use in...	6 kDa	ABY-025
Affilin Affilin Affilins are genetically engineered proteins with the ability to selectively bind antigens. They are structurally derived from one of two proteins, gamma-B crystallin or ubiquitin, both occurring in humans. Affilins are constructed by modification of near-surface amino acids of these proteins and... s	Gamma-B crystallin	20 kDa
	Ubiquitin Ubiquitin Ubiquitin is a small regulatory protein that has been found in almost all tissues of eukaryotic organisms. Among other functions, it directs protein recycling.Ubiquitin can be attached to proteins and label them for destruction...	10 kDa	SPVF 2801
Affitin Affitin Affitins are artificial proteins with the ability to selectively bind antigens. They are structurally derived from the DNA binding protein Sac7d, found in Sulfolobus acidocaldarius, a microorganism belonging to the archaea domain... s	Sac7d (from 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)	7 kDa
Anticalin Anticalin Anticalins are artificial proteins that are able to bind to antigens, either to proteins or to small molecules. They are not structurally related to antibodies, which makes them a type of antibody mimetic. Instead, they are derived from human lipocalins which are a family of naturally binding... s	Lipocalin Lipocalin The lipocalins are a family of proteins which transport small hydrophobic molecules such as steroids, bilins, retinoids, and lipids. They share limited regions of sequence homology and a common tertiary structure architecture... s	20 kDa
Avimer Avimer Avimers are artificial proteins that are able to specifically bind to certain antigens via multiple binding sites. Since they are not structurally related to antibodies, they are classified as a type of antibody mimetic... s	A domains Protein domain A protein domain is a part of protein sequence and structure that can evolve, function, and exist independently of the rest of the protein chain. Each domain forms a compact three-dimensional structure and often can be independently stable and folded. Many proteins consist of several structural...  of various membrane receptors	9–18 kDa
DARPin DARPin DARPins are genetically engineered antibody mimetic proteins typically exhibiting highly specific and high-affinity target protein binding. They are derived from natural ankyrin proteins and consist of at least three, usually four or five repeat motifs of these proteins... s	Ankyrin repeat Ankyrin repeat The ankyrin repeat is a 33-residue motif in proteins consisting of two alpha helices separated by loops, first discovered in signaling proteins in yeast Cdc10 and Drosophila Notch. Ankyrin repeats mediate protein–protein interactions and are among the most common structural motifs in known proteins...  motif	10–19 kDa	MP0112
Fynomers	SH3 domain SH3 domain The SRC Homology 3 Domain is a small protein domain of about 60 amino acids residues first identified as a conserved sequence in the viral adaptor protein v-Crk and the non-catalytic parts of enzymes such as phospholipase and several cytoplasmic tyrosine kinases such as Abl and Src...  of Fyn FYN Proto-oncogene tyrosine-protein kinase Fyn is an enzyme that in humans is encoded by the FYN gene.This gene is a member of the protein-tyrosine kinase oncogene family. It encodes a membrane-associated tyrosine kinase that has been implicated in the control of cell growth...	7 kDa
Kunitz domain peptides	Kunitz domains of various protease inhibitor Protease inhibitor (biology) In biology and biochemistry, protease inhibitors are molecules that inhibit the function of proteases. Many naturally occurring protease inhibitors are proteins.... s	6 kDa	Ecallantide Ecallantide Ecallantide is a drug used for the treatment of hereditary angioedema and in the prevention of blood loss in cardiothoracic surgery. It is an inhibitor of the protein kallikrein and a 60-amino acid polypeptide which was developed from a Kunitz domain through phage display to mimic antibodies...
Monobodies Monobody Monobodies, also known as adnectins, are genetically engineered proteins that are able to bind to antigens. Despite their name, they are not structurally related to antibodies, which makes them a type of antibody mimetic. They are being developed by Adnexus, a biotechnology company which has been...	10th type III domain Fibronectin type III domain The Fibronectin type III domain is an evolutionary conserved protein domain that is widely found in animal proteins. The fibronectin protein in which this domain was first identified contains 16 copies of this domain. The domain is about 100 amino acids long and possesses a beta sandwich...  of fibronectin Fibronectin Fibronectin is a high-molecular weight glycoprotein of the extracellular matrix that binds to membrane-spanning receptor proteins called integrins. In addition to integrins, fibronectin also binds extracellular matrix components such as collagen, fibrin and heparan sulfate proteoglycans...	10 kDa	Angiocept