title: Impact of site-specific N-glycosylation on cellular secretion, activity and specific activity of the plasma phospholipid transfer protein.
abstract: The plasma phospholipid transfer protein (PLTP) plays a key role in lipid and lipoprotein metabolism. It has six potential N-glycosylation sites. To study the impact of these sites on PLTP secretion and activity, six variants containing serine to alanine point mutations were prepared by site-directed mutagenesis and expressed in Chinese hamster ovary Flp-In cells. The apparent size of each of the six PLTP mutants was slightly less than that of wild type by Western blot, indicating that all six sites are glycosylated or utilized. The size of the carbohydrate at each N-glycosylation site ranged from 3.14 to 4.2kDa. The effect of site-specific N-glycosylation removal on PLTP secretion varied from a modest enhancement (15% and 60%), or essentially no effect, to a reduction in secretion (8%, 14% and 32%). Removal of N-glycosylation at any one of the six glycosylation sites resulted in a significant 35-78% decrease in PLTP activity, and a significant 29-80% decrease in PLTP specific activity compared to wild type. These data indicate that although no single N-linked carbohydrate chain is a requirement for secretion or activity, the removal of the carbohydrate chains had a quantitative impact on cellular secretion of PLTP and its phospholipid transfer activity.
authors.affiliation: Northwest Lipid Metrobolism and Diabetes Research Laboratories, Division of Metabolism, Endocrinology, and Nutrition, Department of Medicine, University of Washington, Seattle, Washington 98109-4517, USA. jja@uw.edu
authors.forename: John J
authors.initials: JJ
authors.lastname: Albers
authors.forename: Joseph R
authors.initials: JR
authors.lastname: Day
authors.forename: Gertrud
authors.initials: G
authors.lastname: Wolfbauer
authors.forename: Hal
authors.initials: H
authors.lastname: Kennedy
authors.forename: Simona
authors.initials: S
authors.lastname: Vuletic
authors.forename: Marian C
authors.initials: MC
authors.lastname: Cheung
mesh_terms: D000409:Alanine / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D019943:Amino Acid Substitution; D000818:Animals; D001665:Binding Sites / Q000235:genetics; D015153:Blotting, Western; D016466:CHO Cells; D002241:Carbohydrates / Q000737:chemistry*; D006224:Cricetinae; D003412:Cricetulus; D017077:Culture Media, Conditioned / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D004797:Enzyme-Linked Immunosorbent Assay; D006031:Glycosylation; D006801:Humans; D016297:Mutagenesis, Site-Directed; D050505:Mutant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D049294:Phospholipid Transfer Proteins / Q000737:chemistry* / Q000378:metabolism*; D012694:Serine / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
chemical_list: D002241:Carbohydrates; D017077:Culture Media, Conditioned; D050505:Mutant Proteins; C493430:PLTP protein, human; D049294:Phospholipid Transfer Proteins; D012694:Serine; D000409:Alanine