quaternary structure

This term is a specialized technical expression used exclusively in biochemistry and molecular biology. It describes the highest level of protein organization, where individual tertiary structures—the three-dimensional folds of single polypeptide chains—assemble into a larger, functional complex. This assembly is typically stabilized by non-covalent interactions such as hydrogen bonds, ionic bonds, and hydrophobic effects.

Because it refers to a specific structural level of a protein, it is used in a descriptive, scientific register. It is distinct from primary, secondary, and tertiary structures, which refer to the sequence, local folding, and overall 3D shape of a single chain, respectively. In a laboratory or academic context, the term implies a focus on the stoichiometry and spatial orientation of these subunits.