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Detection of the Heterogeneous O-Glycosylation Profile of MT1-MMP Expressed in Cancer Cells by a Simple MALDI-MS Method

PLoS ONE 7・8・e43751・2012
Takuya Shuo1, Naohiko Koshikawa1, Daisuke Hoshino1, Tomoko Minegishi1, Hiroko Ao-Kondo2, Masaaki Oyama2, Sadanori Sekiya3, Shinichi Iwamoto3, Koichi Tanaka3, Motoharu Seiki1
1: Division of Cancer Cell Research, Institute of Medical Science, 2: Medical Proteomics Laboratory, Institute of Medical Science, 3: Koichi Tanaka Mass Spectrometry Research Laboratory, Shimadzu Corporation

Glycosylation is an important and universal post-translational modification for many proteins, and regulates protein functions. However, simple and rapid methods to analyze glycans on individual proteins have not been available until recently. A new technique to analyze glycopeptides in a highly sensitive manner by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) using the liquid matrix 3AQ/CHCA was developed recently and we optimized this technique to analyze a small amount of transmembrane protein separated by SDS-PAGE.

We used the MALDI-MS method to evaluate glycosylation status of membrane-type 1 matrix metalloproteinase (MT1-MMP). Glycosylation of MT1-MMP is reported to modulate its protease activity and thereby to affect cancer cell invasion. After in-gel tryptic digestion of the protein, a single droplet of the digest was applied directly to the liquid matrix on a MALDI target plate. Concentration of hydrophilic glycopeptides within the central area occurred due to gradual evaporation of the sample solution, whereas nonglycosylated hydrophobic peptides remained at the periphery. This specific separation and concentration of the glycopeptides enabled comprehensive analysis of the MT1-MMP glycosylation.

Thus, we demonstrate heterogeneous glycosylation profile of a protein by a whole protein analysis using MALDI-MS. Since cancer cells are reported to have altered glycosylation of proteins, this easy-to-use method for glycopeptide analysis opens up the possibility to identify specific glycosylation patterns of proteins that can be used as new biomarkers for malignant tumors.