Patterns of Folding and Association of Polypeptide Chains

Abstract

Six levels of structural organization can be distinguished. According to Linderström-Lang (176), four levels of structural organization in proteins can be distinguished: primary, secondary, tertiary, and quaternary structure (176). These terms refer to the amino acid sequence, the regular arrangements of the polypeptide backbone, the three-dimensional structure of the globular protein, and the structures of aggregates of globular proteins, respectively. With our present knowledge, two more levels can be added: supersecondary structures denoting physically preferred aggregates of secondary structure and domains referring to those parts of the protein which form well-separated globular regions. An organizational scheme is given in Figure 5–1a. Since renaturation experiments have shown that the amino acid sequence contains the entire structural information (177), the relationship between these levels is dependent, with elements at a lower level determining the elements of higher levels.