The protein quaternary structure is the arrangement of multiple polypeptide chains in a functional assembly. A single-chain protein has protein tertiary structure without requiring protein quaternary structure. For an exact bookkeeping example, two intact model chains of twelve amino acid residues each contain residues and peptide bonds. Assembly alone adds no peptide bond joining their ends. Stable functional assembly should also be distinguished from protein aggregation. See Alberts et al.: proteins as assemblies of polypeptide subunits.
A protein complex is an assembly of associated proteins. Its composition specifies component identities and their stoichiometry; variable accessory occupancy and transient partners can make the assembly a population of related forms rather than one fixed object.
A vesicle-tethering complex connecting membrane traffic to a selected cell surface. Recruitment to an apical initiation site helps coordinate delivery during epithelial lumen formation.
A cellulosome organizes multiple carbohydrate-degrading enzymes on a scaffold. Local cooperation, substrate attachment and diffusion constraints jointly influence its performance.
ERMES is the yeast ER–mitochondria encounter structure, a contact-associated complex. Synthetic-tether rescue and lipid-conversion assays help distinguish its architectural and functional contributions.
Articles by others on the same topic
Protein quaternary structure refers to the highest level of structural organization in proteins, where two or more polypeptide chains, known as subunits, come together to form a larger, functional protein complex. Each subunit in a quaternary structure can consist of one or more polypeptide chains, and these subunits can be identical (homomeric) or different (heteromeric).