The role of prohormone convertase-2 in hypothalamic neuropeptide processing: a quantitative neuropeptidomic study

Prohormone convertase (PC) 1/3 and 2 are involved in the generation of neuropeptides from their precursors. A quantitative peptidomic approach was used to explore the role PC2 plays in the processing of hypothalamic peptides. In this approach, extracts from mice lacking PC2 activity and from wild-type littermates were labeled with isotopic tags, combined, fractionated on a reverse phase HPLC column, and analyzed by electrospray ionization mass spectrometry. Altogether, 53 neuropeptides or other peptides derived from secretory pathway proteins were identified and sequenced using tandem mass spectrometry. These peptides arise from 21 distinct proteins: proenkephalin, proopiomelanocortin, prodynorphin, protachykinin A and B, procholecystokinin, promelanin-concentrating hormone, proneurotensin, proneuropeptide Y, provasopressin, pronociceptin/orphanin, prothyrotropin-releasing hormone, cocaine- and amphetamine-regulated transcript, chromogranin A and B, secretogranin II, prohormone convertase 1 and 2, propeptidyl-amidating monooxygenase, and proteins designated proSAAS and VGF. Approximately one third of the peptides found in wild-type mice were not detectable in PC2 knock-out mice, and another third were present at levels ranging from 25 to 75% of wild-type levels. Comparison of the cleavage sites suggests that sequences with a Trp, Tyr and/or Pro in the P1' or P2' position, or a basic residue in the P3 position, are preferentially cleaved by PC2 and not by other enzymes present in the secretory pathway.