Abstract
Carcinoembryonic antigen (CEA) of human plasma is a biomarker of many cancer diseases, and its N-glycosylation accounts for 60% of molecular mass. It is highly desirable to characterize its glycoforms for providing additional dimension of features to increase its performance in prognosis and diagnosis of cancers. However, to systematically characterize its site-specific glycosylation is challenging due to its low abundance. Here, we developed a highly sensitive strategy for in-depth glycosylation profiling of plasma CEA through chemical proteomics combined with multi-enzymatic digestion. A trifunctional probe was utilized to generate covalent bond of plasma CEA and its antibody upon UV irradiation. As low as 1 ng/mL CEA in plasma could be captured and digested with trypsin and chymotrypsin for intact glycopeptide characterization. Twenty six out of 28 potential N-glycosylation sites were well identified, which were the most comprehensive N-glycosylation site characterization of CEA on intact glycopeptide level as far as we known. Importantly, this strategy was applied to the glycosylation analysis of plasma CEA in cancer patients. Differential site-specific glycoforms of plasma CEA were observed in patients with colorectal carcinomas (CRC) and lung cancer. The distributions of site-specific glycoforms were different as the progression of CRC, and most site-specific glycoforms were overexpressed in stage II of CRC. Overall, we established a highly sensitive chemical proteomic method to profile site-specific glycosylation of plasma CEA, which should generally applicable to other well-established cancer glycoprotein biomarkers for improving their cancer diagnosis and monitoring performance.
In Brief A chemical proteomic approach for glycosylation profiling of proteins was established for glycosylation characterization of plasma CEA with low abundance. Although CEA has been widely used in diagnosis and prognosis of many cancers, it lacks specificity and sensitivity. We found that the glycosylation of CEA on intact glycopeptide level provided additional dimension of molecular features to improve the performance of CEA in cancer diagnosis and progression.
Highlights
A chemical proteomic approach for glycosylation profiling of proteins with low abundance
Glycosylation identification of plasma CEA on intact glycopeptide level with high sensitivity and reproducibility
Glycosylation features of plasma CEA in cancer patients with CRC and lung cancer and in CRC patients at different progression stages
Competing Interest Statement
The authors have declared no competing interest.
Abbreviations
- CEA
- carcinoembryonic antigen;
- DDA
- data-dependent acquisition;
- PRM
- parallel reaction monitoring;
- CRC
- colorectal cancer;
- CV
- coefficients of variation;
- MS
- mass spectrometry;
- GPSMs
- glycopeptide-spectrum matches;
- FDR
- false discovery rate;
- FA
- formic acid;
- LC
- liquid chromatography;
- ACN
- acetonitrile;
- ZIC-HILIC
- zwitterionic hydrophilic interaction liquid chromatography;
- HCD
- higher energy collision-induced dissociation.
