Homomultimers

Homomultimers are protein complexes formed from multiple copies of the same polypeptide chain. All subunits in a homomultimer are identical, distinguishing them from heteromultimers, which contain different subunits. The oligomeric state can range from dimers and trimers to tetramers and larger assemblies, often arranged with defined symmetry.

Subunit interfaces are typically noncovalent, including hydrophobic contacts, hydrogen bonding, and electrostatic interactions; in some cases, covalent disulfide bonds contribute to stability. Assembly can be influenced by concentration, pH, ionic strength, ligands, or cofactors and may proceed cooperatively. Many homomultimers exist in dynamic equilibria with their monomeric or smaller oligomeric forms, and some form higher-order structures such as cages or chambers.

Functional roles of homomultimers include enhanced stability, cooperative or allosteric regulation of activity, and the creation of catalytic or binding sites at subunit interfaces. Oligomerization can also enable pore formation or channel activity in membrane proteins. Because of their symmetric architecture, homomultimers are common subjects of structural studies and often serve as models for understanding protein-protein interactions.

Examples of well-characterized homomultimers include triosephosphate isomerase, which functions as a homodimer; citrate synthase in many species, a homodimer; CuZn superoxide dismutase, a homodimer; and glutamine synthetase, which can form a dodecamer composed of twelve identical subunits. Disruption of subunit interfaces can impair function and is implicated in various diseases; conversely, controlled homomer assembly is exploited in biotechnology for stabilizing enzymes and designing nanoscale protein architectures.

See also: oligomer, homo-oligomer, protein-protein interactions.