Characterization of recombinant sLDLR^CR1-7. (A) Domain organization of full-length LDLR (top) and of the recombinant soluble ligand-binding fragment sLDLR^CR1-7 (bottom). Ligand-binding domain that harbors complement-type repeats 1 to 7, EGF precursor (EGFP) domain that contains EGF-like modules (A-C) and a beta-propeller domain comprising 6 YWTD motifs (Y), O-linked sugar domain, transmembrane domain, cytoplasmic tail, immunopurification tag, and amino acid residue numbers are indicated. (B) Coomassie brilliant blue–stained 10% (vol/vol) SDS-PAGE analysis of the purified recombinant sLDLR^CR1-7 (lane 1). Immunoblotting of the purified recombinant sLDLR^CR1-7 using an anti–human LDLR antibody followed by 3,3-diaminobenzidine staining (lane 2). Molecular weight standard is indicated. (C) Purified sLDLR^CR1-7 (250 nM) was incubated with immobilized isolated human LDL, HDL, and recombinant RAP (1 μg/well). Binding was detected using the peroxidase-conjugated monoclonal antibody CLB-CAg 69. Data represent the mean ± SD of 3 separate experiments.