Identification of Oxidation Sites and Covalent Cross-Links in Metal Catalyzed Oxidized Interferon Beta-1a: Potential Implications for Protein Aggregation and Immunogenicity

Publication Type:

Journal Article


Molecular pharmaceutics, Volume 10, Issue 6, pp. 2311–2322 (2013)


1543-8392 (Electronic)15

DOI Name (links to online publication)



Oxidation via Cu2+/ascorbate of recombinant human interferon beta-1a (IFNbeta1a) leads to highly immunogenic aggregates, however it is unknown which amino acids are modified and how covalent aggregates are formed. In the present work we mapped oxidized and cross-linked amino acid residues in aggregated IFNbeta1a, formed via Cu2+/ascorbate catalyzed oxidation. Size exclusion chromatography (SEC) was used to confirm extensive aggregation of oxidized IFNbeta1a. Circular dichroism and intrinsic fluorescence spectroscopy indicated substantial loss of secondary and tertiary structure, respectively. Derivatization with 4-(aminomethyl)benzenesulfonic acid was used to demonstrate, by fluorescence in combination with SEC, the presence of tyrosine (Tyr) oxidation products. High performance liquid chromatography coupled to electrospray ionization mass spectrometry of reduced, alkylated, and digested protein was employed to localize chemical degradation products. Oxidation products of methionine, histidine, phenylalanine (Phe), tryptophan, and Tyr residues were identified throughout the primary sequence. Covalent cross-links via 1,4- or 1,6-type addition between primary amines and DOCH (2-amino-3-(3,4-dioxocyclohexa-1,5-dien-1-yl)propanoic acid, an oxidation product of Phe and Tyr) were detected. There was no evidence of disulfide bridge, Schiff base, or dityrosine formation. The chemical cross-links identified in this work are most likely responsible for the formation of covalent aggregates of IFNbeta1a induced by oxidation, which have previously been shown to be highly immunogenic.