N-LINKED OLIGOSACCHARIDE PROFILING OF ONE SAMPLE

这个子项目是众多研究子项目之一

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. Methods: The sample seemed to contain detergents (Triton, Tween and so on...), which may interfere with the sample analysis, so the sample was washed with acetone to make sure to remove all detergents before we analyze the sample by mass spectrometry. The detailed procedures used for your sample are shown below. Acetone precipitation Acetone was added to the dried sample. The sample solution was placed on ice for 15 minutes and then spun at maximum speed in a refrigerated microcentrifuge for 15 minutes to pellet the protein. The supernatant was removed. The sample was washed three times. Release of N-linked glycans The dried sample was dissolved in Trypsin buffer (0.1M Tris-HCl, pH 8.2 containing 0.01M CaCl2). The sample then was denatured by heating for 5 minutes at 100¿C. After cooling, the sample was digested with the trypsin (37oC, overnight). After tryptic digestion, the sample was heated at 100¿ C for 5 minutes to de-activate the trypsin. After cooling to room temperature, the sample was applied to a C18 sep-pak cartridge. Before elution of glycopeptides and peptides, the sample adsorbed in the C18 sep-pak cartridge was cleaned with 5% acetic acid to remove any possible contaminants (salts, etc.). Peptides and glycopeptides then were eluted in series with 20% iso-propanol in 5% acetic acid, 40% iso-propanol in 5% acetic acid and 100% iso-propanol each into a microcentrifuge tube. The propanol fractions were dried and then combined in one tube. The sample was reconstituted with 50mM sodium phosphate buffer (pH 7.5) and then the N-glycans were released using PNGase F (New England BioLabs). After digestion, the sample was passed through a C18 reversed phase cartridge and the carbohydrate fraction was eluted with 5% acetic acid and dried by lyophilization. Released N-linked oligosaccharides were permethylated based on the method of Anumula and Taylor (Anumula and Taylor, 1992) and profiled by mass spectrometry. Mass spectrometry MALDI/TOF-MS analysis was performed in the reflector positive ion mode using ¿-dihyroxybenzoic acid (DHBA, 20mg/mL solution in 50%methanol: water) as a matrix. All spectra were obtained by using a 4700 Proteomics analyzer (Applied Biosystems). NSI-MSn analysis was performed following the method developed at the Complex Carbohydrates Research Center (Aoki K, Perlman M, Lim JM, Cantu R, Wells L, Tiemeyer M. J Biol Chem. 2007 Mar 23;282(12):9127-42.). Mass analysis was determined by using on a LTQ Orbitrap XL mass spectrometer (ThermoFisher) equipped with a nanospray ion source. Permethylated glycans were dissolved in 1mM NaOH in 50% methanol and infused directly into the instrument at a constant flow rate of 0.4 ¿L/ min. A full FTMS spectrum was collected at 60 000 resolution. The capillary temperature was set at 210oC and MS analysis was performed in the positive ion mode. For total ion mapping, automated MS/MS analysis (at 28 collision energy), m/z range, 500 to 2000 was scanned with ITMS mode in successive 2.8 mass unit windows that overlapped the preceding window by 2 mass units.