Kvartäärirakenteessa

Kvartäärirakenteessa, often translated as "in quaternary structure," refers to the arrangement and interaction of multiple polypeptide chains, or subunits, that form a functional protein complex. Proteins composed of more than one polypeptide chain are called oligomeric proteins, and their higher-order organization is known as their quaternary structure. This level of organization is distinct from primary (amino acid sequence), secondary (alpha-helices and beta-sheets), and tertiary (overall 3D folding of a single polypeptide) structures.

The subunits in a quaternary structure can be identical (homo-oligomers) or different (hetero-oligomers). They are held together by various non-covalent interactions, including hydrogen bonds, ionic bonds, hydrophobic interactions, and van der Waals forces. In some cases, disulfide bonds between subunits can also contribute to the stability of the quaternary structure. The specific arrangement of these subunits is crucial for the protein's function, as it can create active sites, allosteric binding sites, or facilitate cooperative binding of ligands. Examples of proteins with significant quaternary structure include hemoglobin, which consists of four subunits that bind oxygen, and antibodies, which are composed of multiple polypeptide chains. Understanding the quaternary structure is essential for comprehending protein function, regulation, and the development of drugs that target protein complexes.