NMR solution structure of the receptor binding domain of human α2- macroglobulin

Abstract

Human α2-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 β-amyloid peptide. We have used NMR spectroscopy on recombinantly expressed uniformly 13C/15N-labeled human RBD to determine its three-dimensional structure in solution. Human RBD is a sandwich of two antiparallel β-sheets, one four-strand and one five-strand, and also contains one α-helix of 2.5 turns and an additional 1-turn helical region. The principal α-helix contains two lysine residues on the outer face that are known to be essential for receptor binding. A calcium binding site (K(d) ~ 11 mM) is present in the loop region at one end of the β-sandwich. Calcium binding principally effects 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 β-amyloid peptide.