Unique autolytic cleavage of human myeloperoxidase. Implications for the involvement of active site MET409.

Deconstruction of Activity-Dependent Covalent Modification of Heme in Human Neutrophil Myeloperoxidase by Multistage Mass Spectrometry (MS4)

“…The sulfonium bond between heme and the sulfur of Met409 was first defined by showing that both it and the Met409−Pro410 peptide bond were cleaved when MPO was treated with 0.16 M sodium acetate (pH 3.8) at 95 °C for 10 min [the original authors termed this reagent 1% acetic acid (pH 3.8)]. 22,23 Applying this treatment to MPO, regardless of thioxanthine 1 treatment, was expected to create a new N-terminus at Pro410 and leave a methyl thioether substituent on the heme pyrrole A ring vinyl group. 22 We used this reaction as the first step in digesting MPO for analysis of chemical changes at the heme group.…”

The Production and Use of Reactive Oxidants by Phagocytes

“…Crystallography shows that the prosthetic group, a tetrapyrrole, lies in a pocket of the heterodimer, its proximal side facing the large polypeptide and its distal side the small polypeptide, though R239, an important arginine from the large polypeptide, also lies near the distal side (Zeng and Fenna, 1992). Glycosylation at two positions on the heavy chain was also seen (Taylor et al, 1992;Zeng and Fenna, 1992). In the full-size protein, the two heterodimers are held together by a single disulfide bond between the two heavy chains.…”

“…The question was finally answered by crystallography, which showed that the tetrapyrrole was a conventional heme residue covalently attached to the enzyme by three separate bonds: ester linkages involving methoxy groups on the A and C rings, and a sulfonium linkage involving a methionine and the ring A vinyl group (Fenna et al, 1995). Furthermore, the ring is not planar, but is bent toward the ester *A sulfonium linkage between myeloperoxidase and its tetrapyrrole was identified by Taylor and colleagues before the crystallographic structure was available (Taylor et al, 1992(Taylor et al, , 1995. linkages (Figure 2, from Fenna et al, 1995), a conformational feature that undoubtedly affects its spectral properties and redox potential.…”