Deglycosylation influences the oxidation activity and antigenicity of myeloperoxidase

Myeloperoxidase (MPO) is pathogenic in ANCA associated vasculitis. It also acts as bactericidal agent. MPO has five N-linked glycosylation sites on its heavy chains. The effect of glycosylation pattern to the functions of MPO is barely known.

We used eight glycosidases to remove different glycans on MPO separately. The chlorination activity of MPO, the binding between ceruloplasmin and MPO, and the reversing effect of MPO-ANCA to this binding were measured. Three de-glycosylated MPOs were used to assay the influence of deglycosylation on microbicidal effect of MPO.

Compared with intact MPO, chlorination activity of deglycosylated MPO declined, in which removing of β-galactopyranoside (0.35 ± 0.02 vs. 0.50 ± 0.04, P < 0.001) and α-linked sialic acid (0.35 ± 0.02 vs. 0.50 ± 0.04, P < 0.001) presented the most significance. Deglycosylation reduced the binding capacity between MPO and its physiological inhibitor-ceruloplasmin, with the most significance on the removal of innermost GlcNAc (0.37 ± 0.04 vs. 1.06 ± 0.11, P < 0.001). Binding between MPO and ceruloplasmin was hardly reversed by MPO-ANCA after deglycosylation, especially on the removal of α-linked sialic acid (71.2 ± 5.1% vs. 88.3 ± 1.0%, P = 0.009), chitobiose core (73.6 ± 1.9% vs. 88.3 ± 1.0%, P = 0.001) and GlcNAc (77.9 ± 1.9% vs. 88.3 ± 1.0%, P = 0.002). Removal of innermost GlcNAc, β-galactopyranoside and α-neuraminidase could weaken the bactericidal effect of MPO, especially the removal of α-neuraminidase (P < 0.001).

Deglycosylation decreased oxidation activity of MPO and its binding with ceruloplasmin. Deglycosylation could also decrease the microbicidal effect of MPO, which might contribute to more severe infections and inflammation. Deglycosylated MPO presented less antigenicity to MPO-ANCA, which indicated the contribution of glycans to MPO epitopes.