Chapter 5 - Quaternary Structure of Proteins

Abstract

The chapter begins by describing the principles that help predict the quaternary structure of an oligomeric protein. It also discusses the association of protein subunits, and helical or continuous protein polymers. Because protein-protein recognition results in a stereochemically constant interaction between protomers, two types of polymers of globular proteins are most often observed: rodlike and closed forms. The rodlike aggregates have helical symmetry. The quaternary structure of closed aggregates with relation to oligomeric enzymes is described in detail in the chapter. Closed form aggregates are also symmetrical, most often using forms of cyclic symmetry. The biological implications of quaternary structure are listed in the chapter along with the details of surface accessibility, or calculating the surface area lost from a protein molecule when the oligomer is formed. The chapter concludes with information on generating coordinates for other subunits. A dimeric protein composed of two identical subunits is nearly always found with two fold rotational symmetry. This symmetrical association optimizes the thermodynamic stabilization occurring between complementary surfaces of the protein subunits.