RESUMO
Capillary zwitterionic-type hydrophilic interaction chromatography (ZIC-HILIC)/ESI-MS has been applied to the Glu-C digest of recombinant human erythropoietin (rhEPO) expressed in Chinese hamster ovary (CHO) cells. N-Glycopeptides (105) and O-glycopeptides (8) were detected in a single run of the capillary ZIC-HILIC/ESI-MS analysis. Among them, N-acetyl-neuraminic acids (Neu5Ac) of N- and O-glycans were partially acetylated and some were replaced with N-glycoyl-neuraminic acid (Neu5Gc). Their retentions in the ZIC-HILIC separation can be explained to some extent with the degree of acetylation and N-glycoylation, both of which influence the hydrophilicity/hydrophobicity of the N- and O-glycan moieties of glycopeptides.
Assuntos
Cromatografia Líquida/métodos , Eritropoetina/química , Glicopeptídeos/isolamento & purificação , Espectrometria de Massas por Ionização por Electrospray/métodos , Sequência de Aminoácidos , Animais , Células CHO , Cricetinae , Cricetulus , Eletroquímica , Eritropoetina/genética , Glicopeptídeos/química , Glicopeptídeos/genética , Glicosilação , Humanos , Dados de Sequência Molecular , Estrutura Molecular , Proteínas Recombinantes , Serina EndopeptidasesRESUMO
A novel chromatographic approach coupling anion-exchange (diethylaminoethylene) and hydrophilic-interaction (amide or zwitterionic type) columns was developed for the separating of 2-pyridylamino derivatives of N-glycans (PA-N-glycans). This is a kind of on-line, two-dimensional (2D) separation approach in hydrophilic-interaction chromatography (called the 2D-HILIC method), analogous to that of coupling cation- (or anion-, or mixed ion-) exchange and reversed-phase columns in hydrophobic interaction (reversed-phase) chromatography. The efficiency of the 2D-HILIC method was tested with biantennary neutral and sialylated PA-N-glycan standards by properly combining linear gradient elutions of water-acetonitrile and spiked-salt (ammonium acetate) elutions. The retention time RSDs of all the peaks in three sequential runs of a 100 min cycle are less than 0.52%, which indicates a reasonably good repeatability of the 2D-HILIC method. Then, the method was applied to a complex mixture of PA-N-glycans from human serum proteins. It was demonstrated that the neutral PA-N-glycans and mono-, di-, tri-, and tetrasialylated PA-N-glycans are able to be eluted in turn according to the number of sialic acids in an automated (programmed) single run.
Assuntos
Aminopiridinas/química , Resinas de Troca Aniônica/química , Cromatografia Líquida/métodos , Polissacarídeos/isolamento & purificação , Cromatografia Líquida/instrumentação , Espectrometria de Massas , Polissacarídeos/químicaRESUMO
Asparagine-linked oligosaccharides (N-glycans) usually show structural heterogeneity, especially in proteins with sialylated N-glycans and, therefore, their structural analysis is still very difficult. A zwitterionic type of hydrophilic interaction chromatography column with sulfobetaine functional groups (called a ZIC-HILIC column) was applied to the separation of tryptic peptides of alpha-1-acid glycoprotein. It was demonstrated that the ZIC-HILIC separation column has a selectivity for sialylated N-glycopeptides and a high capability for separation based on the structural recognition of sialylated N-glycan isomers as well as for the previously reported neutral N-glycans and N-glycopeptides. The retention characteristics of neutral and sialylated N-glycans derivatized with 2-aminopyridine (PA N-glycans) demonstrate that the retentions of the N-glycans are based primarily on hydrophilic interaction with the water-rich liquid layer generated on the surface of the ZIC-HILIC column. In addition, the electrostatic repulsion interaction shielded with counter ions effectively tunes the separation and recognition of sialylated N-glycan isomers.
Assuntos
Técnicas de Química Analítica/métodos , Cromatografia/métodos , Glicopeptídeos/química , Espectrometria de Massas/métodos , Aminopiridinas/análise , Aminopiridinas/química , Betaína/análogos & derivados , Betaína/química , Técnicas de Química Analítica/instrumentação , Glicopeptídeos/análise , Ácido N-Acetilneuramínico/química , Oligossacarídeos/química , Peptídeos/química , Polissacarídeos/química , Espectrometria de Massas por Ionização por Electrospray , Eletricidade Estática , Fatores de TempoRESUMO
Isomeric oligosaccharides and isomeric glycopeptides are sometimes difficult to separate on normal-phase (NP) and reversed-phase (RP) columns. A zwitterionic type of hydrophilic-interaction chromatography column with sulfobetaine groups (called ZIC-HILIC column) was first applied to the separation of 2-aminopyridine derivatized (PA) N-glycans and tryptic peptides of human serum immunoglobulin G (IgG). It is shown that the ZIC-HILIC column has high capability for structural recognition of isomeric N-glycans as well as high selectivity for glycopeptides. The former feature (i.e., structural recognition) was proven by sufficient separation of neutral PA N-glycan isomers, which are usually difficult to separate on NP and RP columns. In addition, it is noteworthy that IgG glycopeptides consisting of isomeric N-glycans and the same peptide sequences can be sufficiently separated on a ZIC-HILIC column. The latter feature (i.e., selectivity) was also demonstrated by easily separating two peptide groups with/without N-glycans. Thus, we note that the ZIC-HILIC column is highly promising for a simple analysis of N-glycans and N-glycopeptide samples.
