Exon 16 del: A novel form of human neutral endopeptidase (CALLA)

The enzyme neutral metalloendopeptidase (E.C. 3.4.24.11), also known as the common acute lymphocytic leukemia antigen, neutral endopeptidase, or enkephalinase, functions as an inactivator of a wide variety of signaling oligopeptides such as substance P, neurokinin A, enkephalins, endothelin, atrial natriuretic factor, and formyl chemotactic peptides. A cDNA clone isolated from a human lung library encodes a fragment of neutral metalloendopeptidase containing an internal 81 base pair deletion when compared with the human placental cDNA for this enzyme. Comparison of the deleted cDNA sequence with the intron-exon structure recently determined as the common acute lymphocytic leukemia antigen reveals that the 81 base pairs corresponds precisely with exon 16. RNA analysis using splice junction oligonucleotides indicates that the 16 del form constitutes a minor but significant fraction of the RNA species present in human lung. Expression of constructs containing 'wild type' and 'exon 16 del' neutral endopeptidases in COS-7 cells reveals that deletion of this 27 amino acid segment reduces enzymatic activity toward the synthetic substrate glutaryl-alanyl-alanyl- phenyl-alanyl-4-methoxy-2-naphthylamide to barely detectable levels.