The role of disulfide bonds in the formation of the spatial structure of the human epidermal growth factor

The epidermal growth factor (EGF) is a peptide of the EGF-like growth factor family with a common conserved EGF-like domain formed by three intramolecular disulfide bonds. This article describes changes in the spatial structure of EGF and its mutant form with the D46G substitution in its C-terminal fragment observed upon disulfide bonds reduction in the corresponding synthetic peptides in a 0.01 M phosphate buffer (pH = 7.4). The structure was analyzed using circular dichroism spectroscopy, spectrofluorimetry, native polyacrylamide gel electrophoresis, and centrifugal ultrafiltration. It was shown that disulfide bonds reduction changes the geometry of the EGF-like domain towards an increase in the content of the beta-structure, while these peptides remain in dimeric form. According to the molecular modeling results, this can lead to the elongation of the main beta-hairpin of the EGF-like domain, to the elongation of the intermolecular beta-structure, or to the formation of a new beta-structure between the N- and C-terminal fragments of each molecule, which will change the intermolecular interface in dimeric form. Disulfide bonds reduction prevents EGF dimer dissociation to monomers. Under physiological conditions, this can lead to the inability of EGF to form binding sites for EGFR (epidermal growth factor receptor) and to cause its activation.