Principles of Protein Structure - G. Schultz 1982

Covalent Structure of Proteins
Mechanisms of Polypeptide Chain Folding and Association

Six levels of Structural Organization of Proteins. According to Linderstrøm-Lang [176], four Levels of Protein structural organization can be distinguished: primary, secondary, tertiary, and quaternary. These terms refer, respectively, to the Amino Acid Sequence, the ordered conformation of the polypeptide backbone, the three-dimensional Structure of a globular protein, and The structure of protein aggregates. Based on our current knowledge, we can add two more levels: Supersecondary structures to denote energetically favored aggregates of Secondary structure, and domains to designate regions that form relatively independent globular modules. The scheme of structural organization is shown in Fig. 5.1.

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Fig. 5.1. LEVELS OF STRUCTURAL organization of Globular proteins.

Protein renaturation experiments have demonstrated that The amino acid sequence contains the complete structural information [177]. Therefore, all levels are interrelated, with the elements of lower levels determining the elements of higher levels.

This interrelation is illustrated as an extremely simplified diagram in Fig. 5.1, b, constructed under the assumption that all types of interactions are clearly delineated, with no interactions occurring between non-adjacent elements in the polypeptide chain or between elements of different levels. To some extent, this framework resembles a hierarchical social system. This chapter will examine all levels of protein structural organization and discuss the relationships among them.