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NMR solution structure of the receptor binding domain of human alpha(2)-macroglobulin
1Department of Biochemistry and Molecular Biology, College of Medicine, University of Illinois at Chicago, Chicago, Illinois 60612-4316, USA.
Abstract:
Human alpha(2)-macroglobulin-proteinase complexes bind to their receptor, the low density lipoprotein receptor-related protein (LRP), through a discrete 138-residue C-terminal receptor binding domain (RBD), which also binds to the beta-amyloid peptide. We have used NMR spectroscopy on recombinantly expressed uniformly (13)C/(15)N-labeled human RBD to determine its three-dimensional structure in solution. Human RBD is a sandwich of two antiparallel beta-sheets, one four-strand and one five-strand, and also contains one alpha-helix of 2.5 turns and an additional 1-turn helical region. The principal alpha-helix contains two lysine residues on the outer face that are known to be essential for receptor binding. A calcium binding site (K(d) approximately 11 mM) is present in the loop region at one end of the beta-sandwich. Calcium binding principally affects this loop region and does not significantly perturb the stable core structure of the domain. The structure and NMR assignments will enable us to examine in solution specific binding of RBD to domains of the receptor and to beta-amyloid peptide.
Insights
Researchers determined the 3D structure of the human alpha(2)-macroglobulin receptor binding domain (RBD) using NMR spectroscopy. This structure reveals a calcium binding site and key residues for binding to the low density lipoprotein receptor-related protein (LRP) and beta-amyloid.
Area of Science:
- Biochemistry
- Structural Biology
- Neuroscience
Background:
- Human alpha(2)-macroglobulin-proteinase complexes interact with the low density lipoprotein receptor-related protein (LRP).
- The C-terminal receptor binding domain (RBD) of alpha(2)-macroglobulin mediates this interaction and also binds beta-amyloid peptide.
- Understanding the RBD structure is crucial for elucidating these binding mechanisms.
Purpose of the Study:
- To determine the three-dimensional structure of the human RBD in solution using NMR spectroscopy.
- To identify structural features, including potential calcium binding sites and key residues involved in receptor and peptide binding.
- To provide structural insights for future studies on binding interactions.
Main Methods:
- Recombinant expression of uniformly (13)C/(15)N-labeled human RBD.
- Nuclear Magnetic Resonance (NMR) spectroscopy for structural determination.
- Analysis of secondary and tertiary structure, including identification of helical and beta-sheet components.
Main Results:
- The 3D structure of human RBD was determined, revealing a beta-sandwich fold with alpha-helical regions.
- A calcium binding site was identified in a loop region, with a dissociation constant (K(d)) of approximately 11 mM.
- Calcium binding was found to primarily affect the loop region without significantly altering the core domain structure.
- Key lysine residues essential for LRP binding were located on the principal alpha-helix.
Conclusions:
- The determined solution structure of human RBD provides a high-resolution model for understanding its interactions.
- The identified calcium binding site and its localized effect suggest a regulatory role in RBD function.
- These structural insights and NMR assignments will facilitate further investigations into the specific binding mechanisms of RBD with LRP and beta-amyloid peptide.