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J Proteome Res. 2005 May-Jun;4(3):889-99.

Afamin is a novel human vitamin E-binding glycoprotein characterization and in vitro expression.

Author information

1
Division of Genetic Epidemiology, Department of Medical Genetics, Clinical and Molecular Pharmacology, Innsbruck Medical University, Schoepfstrasse 41, A-6020 Innsbruck, Austria.

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.

PMID:
15952736
DOI:
10.1021/pr0500105
[Indexed for MEDLINE]

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