A Sulfated, Phosphorylated 7 kDa Secreted Peptide Characterized by Direct Analysis of Cell Culture Media Steven W. Taylor,* Chengzao Sun, Amy Hsieh, Nancy L. Andon, and Soumitra S. Ghosh Amylin Pharmaceuticals, Inc., 9360 Towne Centre Drive, San Diego, California 92121 Received July 13, 2007
Abstract: An unusual sulfotyrosine-, phosphoserinecontaining motif was mapped on a differentially posttranslationally modified 60 residue antimicrobial neuroendocrine peptide called chrombacin. The study was performed by high resolution FT MS using complementary fragmentation techniques. The peptide was analyzed at low levels directly from cell culture media in contrast to previous reports that required extensive purification and proteolytic digestion. The sulfation site was not previously described nor predicted by informatic analysis of the peptide’s precursor sequence. Keywords: chromogranin • FT-MS • insulinoma • peptidomics • post-translational modification
Introduction Bioactive peptide discovery and structural elucidation has traditionally involved collection of a large amount of source material followed by subfractionation and chromatographic purification monitoring enrichment of a specific activity. Today, the sensitivity of mass spectrometry (MS) allows peptide sequence characterization using much smaller amounts of material (
