TY - JOUR
T1 - Mapping N-Terminus Phosphorylation Sites and Quantitation by Stable Isotope Dimethyl Labeling
AU - Wu, Chin Jen
AU - Hsu, Jue Liang
AU - Huang, Sheng Yu
AU - Chen, Shu Hui
N1 - Funding Information:
The authors thank the National Science Council of Taiwan for grant support. They also thank Professor Wen-Chang Chang and Professor Mei-Ling Tsai of the Medical College of National Cheng Kung University for preparing A431 cell lysate and tissue homogenate from late gestation rat uteri.
Copyright:
Copyright 2010 Elsevier B.V., All rights reserved.
PY - 2010/3
Y1 - 2010/3
N2 - We have previously coupled stable isotope dimethyl labeling with IMAC enrichment for quantifying the extent of protein phosphorylation in vivo. The enhanced a1 signal of dimethylated peptides served as a unique mass tag for unequivocal identification of the N-terminal amino acids. In this study, we demonstrate that the a1 ion could further assist in mapping the precise phosphorylation site near the N-terminal region and allow the determination of the exact site and level of phosphorylation in one step by stable isotope dimethyl labeling. We show that the a1 ion signal was suppressed for dimethylated peptides with a phosphorylation site at the N-terminus Ser/Thr residue (N-p*Ser/Thr) but was still enhanced for N-terminus Tyr residue (N-p*Tyr) or internal Ser/Thr residues (-p*Ser/Thr). Based on the dominant de-phosphorylated molecular ions and b-H3PO4 ions for N-p*Ser/Thr, we propose that dimethyl labeling increases the basicity of the N-terminus and accelerates the de-phosphorylation for N-p*Ser/Thr precursors, which, however, suppresses the a1 ion enhancement due to the resulting unsaturated covalent bond on Cα of the N-terminus amino acid. Using this method, we excluded three Ser/Thr phosphorylation sites in A431 cells, two of which, however, were previously reported to be phosphorylation sites; we confirmed three known phosphorylation sites in A431 cells and quantified their ratios upon EGF treatment. Notably, we identified a novel phosphorylation site on Ser43 residue at N-terminus of the tryptic peptide derived from SVH protein in pregnant rat uteri. SVH protein has not been reported or implied with any phosphorylation event, and our data show that the Ser43 of SVH is an intrinsic phosphorylation site in pregnant rat uteri and that its phosphorylation level was slightly decreased upon c-AMP treatment.
AB - We have previously coupled stable isotope dimethyl labeling with IMAC enrichment for quantifying the extent of protein phosphorylation in vivo. The enhanced a1 signal of dimethylated peptides served as a unique mass tag for unequivocal identification of the N-terminal amino acids. In this study, we demonstrate that the a1 ion could further assist in mapping the precise phosphorylation site near the N-terminal region and allow the determination of the exact site and level of phosphorylation in one step by stable isotope dimethyl labeling. We show that the a1 ion signal was suppressed for dimethylated peptides with a phosphorylation site at the N-terminus Ser/Thr residue (N-p*Ser/Thr) but was still enhanced for N-terminus Tyr residue (N-p*Tyr) or internal Ser/Thr residues (-p*Ser/Thr). Based on the dominant de-phosphorylated molecular ions and b-H3PO4 ions for N-p*Ser/Thr, we propose that dimethyl labeling increases the basicity of the N-terminus and accelerates the de-phosphorylation for N-p*Ser/Thr precursors, which, however, suppresses the a1 ion enhancement due to the resulting unsaturated covalent bond on Cα of the N-terminus amino acid. Using this method, we excluded three Ser/Thr phosphorylation sites in A431 cells, two of which, however, were previously reported to be phosphorylation sites; we confirmed three known phosphorylation sites in A431 cells and quantified their ratios upon EGF treatment. Notably, we identified a novel phosphorylation site on Ser43 residue at N-terminus of the tryptic peptide derived from SVH protein in pregnant rat uteri. SVH protein has not been reported or implied with any phosphorylation event, and our data show that the Ser43 of SVH is an intrinsic phosphorylation site in pregnant rat uteri and that its phosphorylation level was slightly decreased upon c-AMP treatment.
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U2 - 10.1016/j.jasms.2009.12.001
DO - 10.1016/j.jasms.2009.12.001
M3 - Article
C2 - 20093040
AN - SCOPUS:76749114813
VL - 21
SP - 460
EP - 471
JO - Journal of the American Society for Mass Spectrometry
JF - Journal of the American Society for Mass Spectrometry
SN - 1044-0305
IS - 3
ER -