Identification and characterization of novel chromogranin B-derived peptides from porcine chromaffin granules by liquid chromatography/electrospray tandem MS.

Chromogranin B (CgB) is a regulated secretory protein that is stored in endocrine and neuroendocrine cells. It can be processed proteolytically to small peptide fragments. In the present study three proteolytic products of porcine CgB were obtained after size-exclusion, immunoaffinity, and reversed-phase chromatography, and then identified by electrospray tandem MS. One novel peptide was identified as S586-R602 (SR-17) and is phosphorylated at one or two serine residues. Another novel peptide H603-Q636 (HQ-34), with molecular mass 3815.56 Da, was found to be oxidized at the methionine residue. In addition, a secretolytin-like peptide fragment (KR-11), which is two amino acids shorter than the bovine secretolytin, was found. This is the first report that the C-terminal region of CgB, the homologue of human CCB, is proteolytically processed further into three small peptide fragments.