Characterization of the vitamin E-binding properties of human plasma afamin.
Human plasma afamin, the fourth member of the albumin gene family, is shown to be a specific binding protein for vitamin E. A radio ligand-binding assay followed by Scatchard and Hill analysis are used to show that afamin has a binding affinity for both alpha-tocopherol and gamma-tocopherol, two of the most important forms of vitamin E, in vitro. The binding-dissociation constant was determined to be 18 microM, indicating that afamin plays a role as vitamin E carrier in body fluids such as human plasma and follicular fluid under physiological conditions. Additionally, we demonstrate that afamin has multiple binding sites for both alpha- and gamma-tocopherol. Due to the large binding capacity of afamin for vitamin E, it might take over the role of vitamin E transport in body fluids under conditions where the lipoprotein system is not sufficient for vitamin E transport. To confirm the experimental results, we performed homology modeling and docking calculations on the predicted tertiary structure, which showed coincidence between calculated and in vitro results.
Voegele
Andreas F
AF
Vitateq Biotechnology GmbH, Innsbruck, Austria.
Jerković
Lidija
L
Wellenzohn
Bernd
B
Eller
Patricia
P
Kronenberg
Florian
F
Liedl
Klaus R
KR
Dieplinger
Hans
H
D001665:Binding Sites; D002352:Carrier Proteins / Q000097:blood / Q000737:chemistry* / Q000378:metabolism; D003198:Computer Simulation; D006023:Glycoproteins; D006801:Humans; D007700:Kinetics; D008958:Models, Molecular; D011485:Protein Binding; D017386:Sequence Homology, Amino Acid; D012709:Serum Albumin / Q000737:chemistry* / Q000378:metabolism; D000075462:Serum Albumin, Human; D013816:Thermodynamics; D014810:Vitamin E / Q000378:metabolism*
C088246:AFM protein, human; D002352:Carrier Proteins; D006023:Glycoproteins; D012709:Serum Albumin; C017763:alpha-tocopherol transfer protein; D014810:Vitamin E; D000075462:Serum Albumin, Human