The higher levels of protein structure are suppoed by

Higher orders of protein structure are stabilized primarily and often exclusively by noncovalent interactions. Principal among these is hydrophobic interactions that drive most hydrophobic amino acid side chains into the interior of the protein away from the surrounding water. Other significant contributors include hydrogen bonds and salt bridges between the carboxylates of aspaic and glutamic acid and the oppositely charged side chains of protonated lysyl, arginyl, and histidyl residues. Some proteins contain covalent disulfide (S&;S) bonds that link the sulfhydryl groups of cysteinyl residues. Formation of disulfide bonds involves oxidation of the cysteinyl sulfhydryl groups and requires oxygen. Intrapolypeptide disulfide bonds fuher enhance the stability of the folded conformation of a peptide, while interpolypeptide disulfide bonds stabilize the quaternary structure of ceain oligomeric proteins.Reference: Explanation: Harper's Biochemistry; 30th edition; Chapter 5; proteins: higher Orders of Structure