Marked differences between metalloproteases meprin A and B in substrate and peptide bond specificity

Meprin A and B are highly regulated, secreted, and cell-surface metalloendo peptidases that are abundantly expressed in the kidney and intestine. Mepri n oligomers consist of evolutionarily related alpha and/or beta subunits. T he work herein was carried out to identify bioactive peptides and proteins that are susceptible to hydrolysis by mouse meprins and kinetically charact erize the hydrolysis. Gastrin-releasing peptide fragment 14-27 and gastrin 17, regulatory molecules of the gastrointestinal tract, were found to be th e best peptide substrates for meprin A and B, respectively. Peptide librari es and a variety of naturally occurring peptides revealed that the meprin p subunit has a clear preference for acidic amino acids in the P1 and P1 ' s ites of substrates. The meprin alpha subunit selected for small (e,g, serin e, alanine) or hydrophobic (e.g, phenylalanine) residues in the P1 and P1 ' sites, and proline was the most preferred amino acid at the P2 ' position. Thus, although the meprin alpha and beta subunits share 55% amino acid ide ntity within the protease domain and are normally localized at the same tis sue cell surfaces, they have very different substrate and peptide bond spec ificities indicating different functions. Homology models of the mouse mepr in alpha and beta protease domains, based on the astacin crystal structure, revealed active site differences that can account for the marked differenc es in substrate specificity of the two subunits.