Ryszard Drożdż

Apolipoprotein E is highly susceptible to oxidation by myeloperoxidase, an enzyme present in the brain

Apolipoprotein E, the most common apolipoprotein found in the brain, is linked to several pathologies like Alzheimers disease. Apolipoprotein E directly binds to beta-amyloid with a strong affinity. Myeloperoxidase, a protein secreted by neutrophils and involved in the inflammatory process, is also present in the brain. In vitro myeloperoxidase oxidation of recombinant human apolipoprotein E leads to fragmentation of the protein with low concentrations of hydrogen peroxide and polymerization with higher concentrations. Comparison with bovine serum albumin shows a higher susceptibility of apolipoprotein E to myeloperoxidase oxidation, which may have importance in the Alzheimers disease process.

Myeloperoxidase-mediated protein oxidation: its possible biological functions.

Abstract Oxidation of proteins occurs both as a side-effect of aerobic energy metabolism and as an effect of specific metabolism of phagocytic polymorphonuclear granulocytes producing O2 −· and H2O2. In contrast to other cells, which control their H2O2 level by degrading it to O2 and H2O, polymorphonuclear neutrophilic leukocytes (PMN) use H2O2 as a substrate for oxidizing chloride ions to HOCl which rapidly react with all neighboring thiol, disulfide and amino residues. Chloramines, which are the most abundant HOCl reaction products, react with proteins, modifying only certain exposed methionine and cysteine residues. This may account for selective inactivation of a number of enzymes, carrier proteins and peptide mediators, including the α1-proteinase inhibitor, α2-macroglobulin and plasminogen activator inhibitor. Inactivaton of plasma proteinase inhibitors protects PMN elastase, collagenase, cathepsin G and other serine proteases in the inflammatory foci. This promotes proteolytic degradation of damaged tissue, removal of bacterial debris and wound healing, as well as tissue remodeling related to the inflammatory processes. Oxidative control of protease-anti-protease balance affects the development of the inflammatory processes. Moreover, inactivation of plasma proteinase inhibitors facilitates primary antigen processing, upregulates lymphocyte proliferative response and activates the local immune response. Oxidation produces a specific protein tagging which attracts and stimulates immune active cells. Therefore, humoral response against oxidatively modified proteins occurs more effectively than that of the native proteins. The effect is dose-dependent with respect to the amount of oxidant employed. Glycol aldehyde, which is the serine chloramine spontaneous decay product, in mice immunized with glycol aldehydemodified egg-white albumin, yields specific IgG production manifold higher than that in mice immunized with native albumin. Immunopotentiation is produced by proliferation expansion of the same immunocompetent clones. Oxidative tagging of proteins may also affect the autoimmune-type reaction. Thus, a growing body of data suggest that the specific role of protein oxidation by activated PMN is oxidative protein tagging facilitating further development of the immune reaction.

Immunoglobulin cleavage by hypochlorous acid treatment.

IgA, IgG and IgM were cleaved by hypochlorous acid treatment. The apparent calculated molecular masses of three polypeptides obtained from IgA were 81.1. 25.8 and 13.9 kDa. The amounts of released IgA fragments were proportional to the amount of HOCl employed. At a HOCl:IgA molar ratio above 320:1, a profound degradation of IgA polypeptide chains occurred, resulting in a yellow-coloured product. The HOCl treatment of IgG resulted in similar effects, the liberation of three fragments, one of them being of a size slightly larger than that of the light chain (30.4 kDa). The treatment of IgM with HOCl also produced three fragments: one corresponding to the monomeric IgM molecule, the second to the light chain (26.4 kDa) and the third of a size smaller than the heavy chain. The optimal protein/HOCl ratios for the degradation of IgG and IgM were 375:1 and 808:1, respectively.

Lysozyme oligomers as a molecular mass standard for sodium dodecyl sulfate-polyacrylamide gel electrophoresis

Egg white lysozyme treated with hypochlorous acid links together producing di-, tri-, tetra-, and pentameric derivatives with molecular masses ranging from 14,300 to 90,500. Similar oligomeric products may be obtained by treating lysozyme color derivatives produced by labeling lysozyme with fluorescein, trinitrobenzenesulfonic acid and 2,4-dinitrofluorobenzene, with hypochlorous acid. The oligomeric lysozyme derivatives thus obtained consist of a mixture of proteins with molecular masses equal to multiples of 14,300 (lysozyme molecular mass). This mixture can be applied as a set of molecular mass standards suitable for determination of protein molecular masses on sodium dodecyl sulfate-polyacrylamide gel electrophoresis.