title: Afamin is a novel human vitamin E-binding glycoprotein characterization and in vitro expression.
abstract: Hydrophobic vitamins are transported in human plasma and extravascular fluids by carrier proteins. No specific protein has been described so far for vitamin E, which plays a crucial role in protecting against oxidative damage and disease. We report here the purification of a 75-kDa glycoprotein with vitamin E-binding properties by stepwise chromatography of lipoprotein-depleted human plasma and monitoring of vitamin E (alpha-tocopherol)-binding activity. Partial sequencing identified this protein as afamin, a previously described member of the albumin gene family with four or five potential N-glycosylation sites. Glycosylation analysis indicated that >90% of the glycans were sialylated biantennary complex structures. The vitamin E-binding properties were confirmed using recombinantly expressed afamin. Qualitative and quantitative analysis of plasma and extravascular fluids revealed an abundant presence of this protein not only in plasma (59.8+/-13.3 microg/mL) but also in extravascular fluids such as follicular (34.4+/-12.7 microg/mL) and cerebrospinal (0.28+/-0.16 microg/mL) fluids, suggesting potential roles for afamin in fertility and neuroprotection. Afamin is partly (13%) bound to plasma lipoproteins. Afamin and vitamin E concentrations significantly correlate in follicular and cerebrospinal fluids but not in plasma. The vitamin E association of afamin in follicular fluid was directly demonstrated by gel filtration chromatography and immunoprecipitation which complements the in vitro findings for purified native and recombinant afamin.
authors.affiliation: Division of Genetic Epidemiology, Department of Medical Genetics, Clinical and Molecular Pharmacology, Innsbruck Medical University, Schoepfstrasse 41, A-6020 Innsbruck, Austria.
authors.forename: Lidija
authors.initials: L
authors.lastname: Jerkovic
authors.forename: Andreas F
authors.initials: AF
authors.lastname: Voegele
authors.forename: Sabine
authors.initials: S
authors.lastname: Chwatal
authors.forename: Florian
authors.initials: F
authors.lastname: Kronenberg
authors.forename: Catherine M
authors.initials: CM
authors.lastname: Radcliffe
authors.forename: Mark R
authors.initials: MR
authors.lastname: Wormald
authors.forename: Eva M
authors.initials: EM
authors.lastname: Lobentanz
authors.forename: Benjie
authors.initials: B
authors.lastname: Ezeh
authors.forename: Patricia
authors.initials: P
authors.lastname: Eller
authors.forename: Norbert
authors.initials: N
authors.lastname: Dejori
authors.forename: Benjamin
authors.initials: B
authors.lastname: Dieplinger
authors.forename: Friedrich
authors.initials: F
authors.lastname: Lottspeich
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Sattler
authors.forename: Manfred
authors.initials: M
authors.lastname: Uhr
authors.forename: Karl
authors.initials: K
authors.lastname: Mechtler
authors.forename: Raymond A
authors.initials: RA
authors.lastname: Dwek
authors.forename: Pauline M
authors.initials: PM
authors.lastname: Rudd
authors.forename: Gottfried
authors.initials: G
authors.lastname: Baier
authors.forename: Hans
authors.initials: H
authors.lastname: Dieplinger
mesh_terms: D001692:Biological Transport; D001826:Body Fluids / Q000737:chemistry; D002352:Carrier Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D002845:Chromatography; D006023:Glycoproteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D006031:Glycosylation; D006801:Humans; D047468:Immunoprecipitation; D008074:Lipoproteins / Q000378:metabolism; D011485:Protein Binding; D012709:Serum Albumin / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D000075462:Serum Albumin, Human; D014810:Vitamin E / Q000378:metabolism*
chemical_list: C088246:AFM protein, human; D002352:Carrier Proteins; D006023:Glycoproteins; D008074:Lipoproteins; D012709:Serum Albumin; D014810:Vitamin E; D000075462:Serum Albumin, Human