Purification and characterization of human endopeptidase 3.4.24.16. Comparison with the porcine counterpart indicates a unique cleavage site on neurotensin

We have purified and characterized human brain endopeptidase 3.4.24.16. The enzyme behaved as a 72 kDa protein and belonged to the metalloprotease family. Human endopeptidase 3.4.24.16 cleaved neurotensin at a unique site at the Pro¹⁰-Tyr¹¹ bond, leading to the formation of neurotensin(1–10) and neurotensin(11–13). The kinetic parameters displayed by human endopeptidase 3.4.24.16 towards a series of natural neuropeptides indicated that bradykinin was the most efficiently proteolysed. Angiotensin I, dynorphins 1–8 and 1–9 and substance P also behaved as good substrates while neuromedin N, angiotensin II, leucine and methionine enkephalin and neurokinin A resisted degradation by human endopeptidase 3.4.24.16. We have purified the porcine counterpart of endopeptidase 3.4.24.16 and compared its ability to cleave neurotensin with that of the enzyme from human origin. It appeared that, besides a major production of neurotensin(1–10), an additional formation of neurotensin(1–8) was observed with the pig enzyme, suggesting a cleavage of neurotensin not only at the Pro¹⁰-Tyr¹¹ bond but also at the Arg⁸-Arg⁹ peptidyl bond. The latter cleavage appeared reminiscent of endopeptidase 3.4.24.15 since this peptidase was reported to cleave neurotensin at the Arg⁸-Arg⁹ bond. Our study indicated that neurotensin(1–10) formation by porcine endopeptidase 3.4.24.16 could be potently blocked with the selective endopeptidase 3.4.24.16 dipeptide inhibitor Pro-Ile without interfering with neurotensin(1–8) formation. By contrast, the formation of the latter product was highly potentiated by dithiothreitol and inhibited by the endopeptidase 3.4.24.15 inhibitor Cpp-Ala-Ala-Tyr-pAB, two effects that were not observed for neurotensin(1–10) production. Altogether, our results indicate that porcine endopeptidase 3.4.24.16 cleaves neurotensin at a unique site, leading to the formation of rteurotensin(1–10) and that the production of neurotensin(1–8) is due to contaminating endopeptidase 3.4.24.15.