Abstract
Human neutrophil microbicidal activity is largely mediated by reactive species generated by the oxygen-dependent myeloperoxidase (MPO) system. Peroxidase-negative neutrophils from many patients with hereditary MPO deficiency possess a 90-kDa MPO-related protein. We recently identified a missense mutation, R569W, in the MPO gene of many subjects with MPO deficiency. In these studies we examined the consequences of R569W on MPO biosynthesis and processing, using stably transfected K562 cells expressing normal MPO or the R569W mutation. K562 cells expressing normal MPO mimicked faithfully many features of MPO biosynthesis in myeloid cells. 1) apopro-MPO was synthesized; 2) a functional heme group was inserted into apopro-MPO, and enzymatically active pro-MPO was thereby generated; 3) pro-MPO underwent proteolytic processing to mature MPO; and 4) hemin augmented the processing of pro-MPO. pREP-R569W cells synthesized apopro-MPO, but heme was not inserted. Neither enzymatically active pro-MPO nor mature MPO was synthesized by transfectants expressing mutated cDNA, confirming our hypothesis that the R569W mutation results in a form of apopro-MPO which does not undergo post-translational processing to enzymatically active MPO species. In addition, these data support previous suggestions that heme insertion into apopro-MPO is necessary for its subsequent proteolytic processing into mature MPO subunits.
Highlights
1 in every 2,000 – 4,000 individuals [19]
We have previously described a series of unrelated individuals with hereditary MPO deficiency whose PMNs lack spectroscopic and enzymatic evidence of functionally active MPO but possess a 90-kDa protein recognized by a monospecific antibody to MPO [20]
In studies using K562 cells transfected with cDNA for normal and for mutated MPO, we describe the effects of the R569W mutation on MPO biosynthesis
Summary
Vol 271, No 16, Issue of April 19, pp. 9546 –9549, 1996 Printed in U.S.A. (Received for publication, December 3, 1995, and in revised form, January 30, 1996). We have previously described a series of unrelated individuals with hereditary MPO deficiency whose PMNs lack spectroscopic and enzymatic evidence of functionally active MPO but possess a 90-kDa protein recognized by a monospecific antibody to MPO [20]. Based on these studies, we speculated that this form of MPO deficiency results from synthesis of an aberrant MPO precursor, which is incorrectly processed posttranslationally [20]. The data suggest that insertion of heme into the peptide backbone of apopro-MPO may be a prerequisite for proteolytic maturation of pro-MPO
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
