title: Characterization of the soluble, secreted form of urinary meprin.
abstract: A soluble form of the kidney membrane metalloendopeptidase, meprin, is present in urine. Urinary meprin is expressed in BALB/C mice with the Mep-1 alpha/alpha genotype (high meprin, expressing meprin-alpha and meprin-beta ) but not in BALB.K mice of the Mep-1b/b genotype (that only express meprin-beta ). Western blotting with antisera specific to the meprin-alpha and the meprin-beta subunits established that the only form of meprin present in urine samples was derived from meprin-alpha. 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 alpha-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.
authors.affiliation: Department of Biochemistry and Applied Molecular Biology, UMIST, Manchester, U.K.
authors.forename: R J
authors.initials: RJ
authors.lastname: Beynon
authors.forename: S
authors.initials: S
authors.lastname: Oliver
authors.forename: D H
authors.initials: DH
authors.lastname: Robertson
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D004792:Enzyme Precursors / Q000737:chemistry / Q000235:genetics; D005260:Female; D007668:Kidney / Q000201:enzymology; D008297:Male; D008666:Metalloendopeptidases / Q000737:chemistry / Q000235:genetics / Q000652:urine*; D051379:Mice; D008807:Mice, Inbred BALB C; D008871:Microvilli / Q000201:enzymology; D008969:Molecular Sequence Data; D015394:Molecular Structure; D012727:Sex Characteristics; D012995:Solubility; D014357:Trypsin
chemical_list: D004792:Enzyme Precursors; D014357:Trypsin; D008666:Metalloendopeptidases; C053833:meprin A