title: A major kinetic trap for the oxidative folding of human epidermal growth factor.
abstract: The folding pathway of human epidermal growth factor (EGF) has been characterized by structural and kinetic analysis of the acid-trapped folding intermediates. Oxidative folding of the fully reduced EGF proceeds through 1-disulfide intermediates and accumulates rapidly as a single stable 2-disulfide intermediate (designated as EGF-II), which represents up to more than 85% of the total protein along the folding pathway. Among the five 1-disulfide intermediates that have been structurally characterized, only one is native, and nearly all of them are bridges by neighboring cysteines. Extensive accumulation of EGF-II indicates that it accounts for the major kinetic trap of EGF folding. EGF-II contains two of the three native disulfide bonds of EGF, Cys(14)-Cys(31) and Cys(33)-Cys(42). However, formation of the third native disulfide (Cys(6)-Cys(20)) for EGF-II is slow and does not occur directly. Kinetic analysis reveals that an important route for EGF-II to reach the native structure is via rearrangement pathway through 3-disulfide scrambled isomers. The pathway of EGF-II to attain the native structure differs from that of three major 2-disulfide intermediates of bovine pancreatic trypsin inhibitor (BPTI). The dissimilarities of folding mechanism(s) between EGF, BPTI, and hirudin are discussed in this paper.
authors.affiliation: Research Center for Protein Chemistry, Institute of Molecular Medicine, The University of Texas, Houston, TX 77030, USA. rowen.chang@uth.tmc.edu
authors.forename: J Y
authors.initials: JY
authors.lastname: Chang
authors.forename: L
authors.initials: L
authors.lastname: Li
authors.forename: P H
authors.initials: PH
authors.lastname: Lai
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D007611:Aprotinin / Q000737:chemistry; D002417:Cattle; D004220:Disulfides / Q000737:chemistry; D004815:Epidermal Growth Factor / Q000737:chemistry*; D006629:Hirudins / Q000737:chemistry; D006801:Humans; D007700:Kinetics; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D004220:Disulfides; D006629:Hirudins; D004815:Epidermal Growth Factor; D007611:Aprotinin