The cysteine residues in the carboxy terminal domain of tropoelastin form an intrachain disulfide bond that stabilizes a loop structure and positively charged pocket

Analysis of purified bovine tropoelastin with Ellman's reagent and [¹⁴C]iodo-acetamide demonstrated that the only two cysteine residues in the molecule form an intrachain disulfide bond. Molecular modeling suggests that the cysteine residues are juxtaposed as the result of a tight turn that produces an antiparallel beta structure. Protruding from the C-terminal end of the turn is the sequence Arg-Lys-Arg-Lys which forms the floor of a positively charged pocket created by the extension of the arginine and lysine side chains on opposite sides of the peptide chain perpendicular to the plane of the turn. The side chain of a conserved lysine residue in the disulfide-bonded loop forms the top of the pocket. This positively charged pocket may define a binding site for acidic microfibrillar proteins that mediate elastic fiber assembly.