tetramer

A tetramer is a molecular assembly composed of four monomer units. The term is used across chemistry and biochemistry to describe both small synthetic oligomers and protein complexes with four subunits. A tetramer can form when four monomers are linked covalently or assembled through noncovalent interactions; the overall architecture may be linear, cyclic, or branched. Subunits may be identical, forming a homotetramer, or distinct, forming a heterotetramer.

In proteins, tetramers are a common form of quaternary structure and often enable cooperative interactions, enhanced stability, and complex regulatory mechanisms. Tetramerization can influence enzymatic activity, substrate affinity, and allosteric control, and it frequently underpins functional organization in cells.

Examples of tetramers in biology include:

- Hemoglobin, a heterotetramer composed of two alpha and two beta subunits, which enables cooperative oxygen binding and release in blood.

- Lactate dehydrogenase, which can form tetramers containing different subunits, producing tissue-specific isoenzymes with varying kinetic properties.

- Streptavidin, a homotetramer whose four identical subunits each bind biotin with very high affinity, widely used in biotechnology for affinity capture and detection.

In non-biological contexts, tetramers also arise in small-molecule chemistry and supramolecular chemistry, where four units assemble to form discrete, well-defined architectures used in catalysis, materials science, and molecular recognition.

See also: oligomer, polymer, quaternary structure, homotetramer, heterotetramer.