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Molecular Structures of Isolevuglandin-Protein Cross-Links

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journal contribution
posted on 07.09.2016, 00:00 by Wenzhao Bi, Geeng-Fu Jang, Lei Zhang, John W. Crabb, James Laird, Mikhail Linetsky, Robert G. Salomon
Isolevuglandins (isoLGs) are stereo and structurally isomeric γ-ketoaldehydes produced through free radical-induced oxidation of arachidonates. Some isoLG isomers are also generated through enzymatic cyclooxygenation. Post-translational modification of proteins by isoLGs is associated with loss-of-function, cross-linking and aggregation. We now report that a low level of modification by one or two molecules of isoLG has a profound effect on the activity of a multi subunit protease, calpain-1. Modification of one or two key lysyl residues apparently suffices to abolish catalytic activity. Covalent modification of calpain-1 led to intersubunit cross-linking. Hetero- and homo-oligomers of the catalytic and regulatory subunits of calpain-1 were detected by SDS–PAGE with Western blotting. N-Acetyl-glycyl-lysine methyl ester and β-amyloid(11–17) peptide EVHHQKL were used as models for characterizing the cross-linking of protein lysyl residues resulting from adduction of iso[4]­LGE2. Aminal, bispyrrole, and trispyrrole cross-links of these two peptides were identified and fully characterized by mass spectrometry. Aminal and bispyrrole dimers were both detected. Furthermore, a complex mixture of derivatives of the bispyrrole cross-link containing one or more additional atoms of oxygen was found. Interesting differences are evident in the predominant cross-link type generated in the reaction of iso[4]­LGE2 with these peptides. More aminal cross-links versus bispyrrole are formed during the reaction of the dipeptide with iso[4]­LGE2. In contrast, more bispyrrole versus aminal cross-links are formed during the reaction of EVHHQKL with iso[4]­LGE2. It is tempting to speculate that the EVHHQKL peptide–pyrrole modification forms noncovalent aggregates that favor the production of covalent bispyrrole cross-links because β-amyloid(11–17) tends to spontaneously oligomerize.

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