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 end ocrine and neuroendocrine cells. It can be processed proteolytically to sma ll peptide fragments. In the present study three proteolytic products of po rcine CgB were obtained after size-exclusion, immunoaffinity, and reversed- phase chromatography, and then identified by electrospray tandem MS. One no vel peptide was identified as S586-R602 (SR-17) and is phosphorylated at on e or two serine residues. Another novel peptide H603-Q636 (HQ-34), with mol ecular 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 am ino acids shorter than the bovine secretolytin, was found. This is the firs t report that the C-terminal region of CgB, the homologue of human CCB, is proteolytically processed further into three small peptide fragments.