The Single Ligand-binding Repeat of Tva, a Low Density Lipoprotein Receptor-related Protein, Contains Two Ligand-binding Surfaces

The receptor for avian sarcoma/leukosis virus subtype A (ASLV-A), Tva, is the simplest member of the low density lipoprotein receptor family containing a single ligand-binding repeat (LBR). Most LBRs contain a central Trp (Trp33 in Tva) that is important for ligand binding and, for the low density l...

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Bibliographic Details
Published in:The Journal of biological chemistry 2006-08, Vol.281 (32), p.22827-22838
Main Authors: Contreras-Alcantara, Susana, Godby, Jesse A., Delos, Sue E.
Format: Article
Language:English
Subjects:
Amino Acid Sequence
Animals
Avian Proteins - chemistry
Avian Proteins - physiology
Binding Sites
Calcium - chemistry
Calcium - metabolism
Chickens
Glycoside Hydrolases - chemistry
Ligands
Models, Molecular
Molecular Sequence Data
Protein Binding
Protein Structure, Tertiary
Quail
Receptors, Virus - chemistry
Receptors, Virus - physiology
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Summary:The receptor for avian sarcoma/leukosis virus subtype A (ASLV-A), Tva, is the simplest member of the low density lipoprotein receptor family containing a single ligand-binding repeat (LBR). Most LBRs contain a central Trp (Trp33 in Tva) that is important for ligand binding and, for the low density lipoprotein receptor, is associated with familial hypercholesterolemia. The Tva ligand-binding module contains a second Trp (Trp48) that is part of a DEW motif present in a subset of LBRs. Trp48 is important for ASLV-A infectivity. A soluble Tva (sTva) ligand-binding module is sufficient for ASLV-A infectivity. Tva interacts with the viral glycoprotein, and a soluble receptor-binding domain (SUA) binds sTva with picomolar affinity. We investigated whether Tva, a retroviral receptor, could behave as a classic LBR by assessing sTva interactions with the universal receptor-associated protein (RAP) and comparing these interactions with those between sTva and its viral ligand (SUA). To address the role of the two Trp residues in Tva function, we prepared sTva harboring mutations of Trp33, Trp48, or both and determined the binding kinetics with RAP and SUA. We found that sTva behaved as a “normal” receptor toward RAP, requiring both calcium and Trp33 for binding. However, sTva binding to SUA required neither calcium nor Trp33. Furthermore, sTva could bind both RAP and SUA simultaneously. These results show that the single LBR of Tva has two ligand-binding sites, raising the possibility that other LBRs may also.
ISSN:0021-9258
1083-351X
DOI:10.1074/jbc.M512599200