Stereochemistry of oligomeric proteins

The subunits of many oligomeric proteins are organized into stable arrays with high symmetry. When these proteins interact with small molecules such as enzyme substrates or inhibitors, a variety of non-equivalent forms of the protein may be produced. Some of these forms have the same atomic composition, but differ in the spatial arrangement of the subunits. These species differ in all of their properties (conformation, affinity for substrate, etc.), and the relationships among them and among their subunits may be defined using stereochemical nomenclature which has been developed for small molecules. In many cases, the number of such forms is quite large. Rigorous, group-theoretical methods for enumerating all possible species are described and illustrated for the enzyme aspartate transcarbamoylase.