Chapter 4 - Three-Dimensional Structure of Proteins

Abstract

The protein structure is defined based upon the four hierarchical structures: primary, secondary, tertiary, and quaternary. The primary structure is the unique sequence of amino acids residues, determined by DNA sequence. Secondary structure consists of four structural motifs: α-helix, β-pleated sheet, β-turns, and non-repetitive structure. Tertiary structure defines the overall three-dimensional conformation, which consists of folding of the motifs to bring together disparate amino acid residues in the assembly of a functional unit. The three-dimensional structure is stabilized by the nature of the R-groups that allows for hydrophobic interactions, to achieve maximum van der Waals forces, electrostatic interactions, and H-bonds. Formation of disulfide covalent bonds between two strategically located cysteine residues stabilizes the folded conformation. Quaternary structure refers to those proteins which consist of more than one polypeptide chain and their assembly into a functional molecule. The chapter also discusses the degradation of protein, which occurs in the body by several different processes.