Identification of oxidative modification of shrimp (Metapenaeus ensis) tropomyosin induced by malonaldehyde

Abstract

In this study, shrimp tropomyosin was subjected to malonaldehyde (MDA)-induced oxidative stress in aqueous situation. The in vivo cross-linking of tropomyosin was evaluated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and the structural changes were investigated by differential scanning calorimetry, circular dichroism, and Fourier transform infrared spectroscopy (FTIR). The location of the resulting protein carbonyls was determined by mass spectrometry. The SDS-PAGE of the cross-linked tropomyosin showed four new bands corresponding to two, three, four, and five-time molecular weights of tropomyosin. The conformational structures were partly destroyed because of the thermal denaturation at higher temperatures. The α-helix content increased, and new chemical bonds were formed by the MDA modification. These physiochemical properties were confirmed by the identification of amino acid side-chain modifications by using liquid chromatography–tandem mass spectrometry. Lysine (Lys), glutamine (Gln), and asparagine (Asn) residues in tropomyosin were modified at four lysine (Lys-76, 168, 189, and 233), five glutamine (Gln-61, 70, 118, 147, and 247), and four asparagine (Asn-17, 107, 203, and 215) sites. Apart from these MDA modification sites, oxidized methionine was observed by data search. These results indicate that some active food ingredients, such as MDA, can react with the side chains of amino acids resulting in structural changes in the protein.