This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Human plasma apolipoprotein E (apoE) is responsible for the clearance of lipoprotein remnants and has been implicated in diseases like familial type III hyperlipoproteinemia and Alzheimer?s disease. It is known to be initially sialylated after synthesis and later desialylated in the plasma. Studies of synthesis and intracellular modification of apoE by HepG2 cells have shown modified apoE isoproteins corresponding to the sialo apoE forms with two, four or six sialic acid residues. The expected O-glycosylation site needs to be confirmed and the kind of modification to be characterized by mass spectrometry. From a tryptic digest of apoE, one disialylated glycan could be detected at the expected position by LC-MS/MS, and was then also found by standard MALDI TOF MS. It is planned to isolate the glycopepitde(s) with the help of lectins. Vibrationally cooled (VC) MALDI FT-MS might help to detect higher sialylated, more instable homologues.
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