title: Effect of sialic acid content on glycoprotein pI analyzed by two-dimensional electrophoresis.
abstract: 2-DE is broadly used for quantitative analysis of differential protein expression in complex mixtures such as serum samples or cell lysates. PTMs directly influence the 2-DE pattern, and knowledge of the rules of protein separation is required in order to understand the protein distribution in a 2-DE gel. Glycosylation is the most common PTM and can modify both the molecular weight and the pI of a protein. In particular, the effect of charged monosaccharides (mainly sialic acids, SAs) on the 2-DE pattern of a protein is of major interest since changes in sialylation are regularly observed in comparative studies. Little is known about the pI shift of a glycoprotein induced by the presence of SAs, or whether this shift is the same for all glycoproteins. To address this issue, this study examined the influence of SA on the 2-DE pattern of three serum glycoproteins (haptoglobin, α1-antitrypsin and ribonuclease 1), which N-glycan chains had been previously characterised, and reviewed existing bibliographic data. The SA content of the different glycoforms of a glycoprotein showed a negative linear correlation with the pI, although the slope varied among the studied glycoproteins. We also described a positive correlation between the protein pI and the pI decrease per SA molecule.
authors.affiliation: Unitat de Bioquímica i Biologia Molecular, Departament de Biologia, Universitat de Girona, Campus de Montilivi s/n, Girona, Spain.
authors.forename: Sílvia
authors.initials: S
authors.lastname: Barrabés
authors.forename: Ariadna
authors.initials: A
authors.lastname: Sarrats
authors.forename: Esther
authors.initials: E
authors.lastname: Fort
authors.forename: Rafael
authors.initials: R
authors.lastname: De Llorens
authors.forename: Pauline M
authors.initials: PM
authors.lastname: Rudd
authors.forename: Rosa
authors.initials: R
authors.lastname: Peracaula
mesh_terms: D000230:Adenocarcinoma / Q000378:metabolism; D000465:Algorithms; D015180:Electrophoresis, Gel, Two-Dimensional / Q000379:methods*; D006023:Glycoproteins / Q000737:chemistry* / Q000378:metabolism; D006031:Glycosylation; D006242:Haptoglobins / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D007526:Isoelectric Point; D016014:Linear Models; D008956:Models, Chemical; D019158:N-Acetylneuraminic Acid / Q000737:chemistry*; D010190:Pancreatic Neoplasms / Q000378:metabolism; D050500:Pancreatitis, Chronic / Q000378:metabolism; D012259:Ribonuclease, Pancreatic / Q000097:blood / Q000737:chemistry / Q000378:metabolism; D000515:alpha 1-Antitrypsin / Q000097:blood / Q000737:chemistry / Q000378:metabolism
chemical_list: D006023:Glycoproteins; D006242:Haptoglobins; D000515:alpha 1-Antitrypsin; D012259:Ribonuclease, Pancreatic; D019158:N-Acetylneuraminic Acid