Jpn. J. Infect. Dis., 57, S13-S14, 2004
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Biosynthesis and Sorting of Myeloperoxidase
in Hematopoietic Cells
Inge Olsson*, Elinor Bulow and Markus Hansson
Department of Hematology, Lund University, Lund, Sweden
*Corresponding author: Inge.Olsson@hematogi.lu.se
SUMMARY: The neutrophil granulocytes have a critical role in innate
immunity through killing of phagocytized microorganisms, in which
myeloperoxidase (MPO) participates. MPO is stored in cytoplasmic
azurophil lysosome-like granules together with other antibiotic
proteins and digestive enzymes. During passage in the secretory
pathway pro-MPO is folded, subjected to oligosaccharide modification,
and retrieval from constitutive secretion to become targeted to
azurophil granules for final processing and storage. Propeptide-deleted
MPO precursor was found not to be processed to mature MPO and
not to be targeted for storage but instead degraded or secreted.
This indicated that the propeptide of the MPO precursor was a
prerequisite for the final processing and granule targeting of
proMPO. When the MPO propeptide was expressed as a chimera with
a normally secretory protein, the ER retention of the chimera
was prolonged compared with that of the native protein. Thus,
the propeptide of MPO precursor may also mediate the normally
long ER-residence of proMPO. Both mature MPO and secreted proMPO
contained complex oligosaccharide side chains indicating that
proMPO and, thus, mature MPO has passed the medial Golgi stack
where complex oligosaccharides are formed, and exited at TGN like
other proteins targeted for azurophil granules.