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Characterization of the soluble, secreted form of urinary meprin

1996; Portland Press; Volume: 315; Issue: 2 Linguagem: Inglês

10.1042/bj3150461

1470-8728

Robert J. Beynon, S. G. Oliver, Duncan H. L. Robertson,

thermodynamics and calorimetric analyses

A soluble form of the kidney membrane metalloendopeptidase, meprin, is present in urine. Urinary meprin is expressed in BALB/C mice with the Mep-1a/a genotype (high meprin, expressing meprin-α and meprin-β) but not in BALB.K mice of the Mep-1b/b genotype (that only express meprin-β). Western blotting with antisera specific to the meprin-α and the meprin-β subunits established that the only form of meprin present in urine samples was derived from meprin-α. This form of meprin is partially active, and comprises at least three variants by non-reducing SDS/PAGE and by zymography and two protein bands on reducing SDS/PAGE. Sequencing of these two bands established that the N-terminus of the larger protein band begins with the pro-peptide sequence of the α-subunit (VSIKH..), whereas the smaller band possessed the mature meprin N-terminal sequence (NAMRDP..). Trypsin is able to remove the pro-peptide, with a concomitant activation in proteolytic activity. After deglycosylation, the size of the pro- and mature forms of urinary meprin are consistent with cleavage in the region of the X–I boundary. There is a pronounced sexual dimorphism in urinary meprin expression. Females secrete a slightly larger form, and its proteolytic activity is about 50% of that released by males. The urinary meprin is therefore a naturally occurring secreted form of this membrane-bound metalloendopeptidase and is more likely to be generated by alternative processing pathways than by specific release mechanisms.