Protein Quaternary Structure: Symmetry Patterns

Abstract

Abstract Protein molecules can assemble into larger, multisubunit oligomers that possess unique quaternary structures and biological properties. The properties of the oligomeric protein can be quite different from those of the individual subunits. The noncovalent protein–protein interactions giving rise to oligomers often result in symmetric complexes containing identical monomers in identical environments. The symmetry properties of these complexes are described, in particular with respect to the types of subunit–subunit interactions giving rise to the oligomers. Because the symmetry of the macromolecular assemblies is based on the symmetric interactions between the subunits, understanding the symmetry provides further insight into the functioning of the oligomers. Specific examples discussed include: aspartate carbamoyltransferase (where symmetry concepts are tied to allosteric control), multienzyme complexes (built along the lines of the Platonic polyhedra) and virus capsids (large macromolecular complexes formed making use of symmetry and quasi‐symmetry).