N-Benzoyl-L-tyrosyl-p-aminobenzoic acid hydrolase beta (human meprinbeta). A 13-amino-acid sequence is required for proteolyticprocessing and subsequent secretion.

ABSTRACT

N-Benzoyl-L-tyrosyl-p-aminobenzoic acid hydrolase or human meprin (PPH) is a brush-border membrane enzyme of small intestinal epithelial cells. It is a type I integral membrane protein composed of two disulphide-bridged subunits (alpha and beta). PPH and its homologous counterparts in rodents belong to the astacin family of zinc-metalloendopeptidases. Although the amino-acid sequence of the beta subunits is 80-90% identical in these three species, processing is different. Expression of PPHbeta in simian virus 40-transformed African green monkey kidney cells (COS-1) and Madin Darby canine kidney (MDCK) cells results in its cell surface localization and secretion, whereas mouse meprinbeta is only found at the plasma membrane. To investigate proteolytic processing of PPHbeta and to identify the cleavage site, different C-terminal domains of wild-type PPHbeta were exchanged with the homologous domains of mouse meprinbeta. We identified a 13-amino-acid sequence (QIQLTPAPSVQDL) necessary for cleavage and subsequent secretion of PPHbeta. Using brefeldin A, the site of processing was identified as being after passage through the Golgi compartment. Proteolytic processing of PPHbeta thus provides a means for secretion of alphabeta heterodimers.