HUMAN AND RAT TESTIS EXPRESS 2 MESSENGER-RNA SPECIES ENCODING VARIANTS OF NRD CONVERTASE, A METALLOENDOPEPTIDASE OF THE INSULINASE FAMILY

Rat testis NRD convertase (EC 3.4.24.61) is a Zn2+-dependent endopepti dase that cleaves, in vitro, peptide substrates at the N-terminus of A rg residues in dibasic sites. This putative processing enzyme of the i nsulinase family of metallopeptidases exhibits a significant degree of similarity to insulinase and two yeast processing enzymes, Axl1 and S te23. We report the cloning of two human testis cDNA species encoding isoforms of NRD convertase, hNRD1 and hNRD2. Whereas the hNRD1 transcr ipt (3.7 kb) is equivalent to the previously characterized rat cDNA (r NRD1), hNRD2 and rNRD2 are 3.9 kb novel forms containing a nucleotide insertion encoding a 68-residue segment. This motif, which is inserted N-terminal of the Zn2+-binding site, HXXEH, is contained within the m ost conserved region among the insulinase family members. Analysis of the deduced primary sequences revealed 92% identity between rat and hu man orthologues. The human gene encoding NRD convertase was localized to chromosome 1p32.1-p32.2. Whereas NRD convertase is mostly expressed in testis and in 24 cell lines, low mRNA. levels were detected in mos t of the 27 other tissues tested.