Hexamers

Hexamer is a molecular assembly composed of six subunits. The term can describe proteins, nucleic acid complexes, or small molecules that aggregate in groups of six. Hexamers may be formed from six identical subunits (homohexamers) or from two or more different subunits (heterohexamers). They often exhibit cyclic (C6) symmetry or dihedral (D3) symmetry, especially when arranged as a ring or as two trimers brought together.

In biology, hexamers are common as functional molecular units. They can provide cooperative interfaces, structural stability, or central pores in channels. Many viral capsids also employ hexameric arrangements; icosahedral viruses often feature hexameric capsomers, clusters of six protein subunits that assemble into the shell.

Characterization of hexamers uses structural and biophysical methods such as X-ray crystallography, cryo-electron microscopy, small-angle X-ray scattering, and analytical ultracentrifugation. Determining whether a protein naturally forms a hexamer, and whether it exists as a hexamer under physiological conditions, is an important aspect of studying quaternary structure and allostery.

Etymology and usage: the word hexamer derives from the Greek hex, meaning six, and meros, meaning part. The term is widely used across biochemistry, molecular biology, and virology to denote six-subunit assemblies.

See also oligomer, protein quaternary structure, viral capsid.