Macrophage scavenger receptors have been implicated in various macrophage-associated processes, including
atherosclerosis and clearance of bacterial
endotoxin. They bind to a wide variety of polyanionic
ligands and display complex binding characteristics. cDNAs from the murine macrophage-like cell line P388D1 encoding the full-length type I and type II murine
scavenger receptors were cloned, sequenced, and expressed in Chinese hamster ovary cells. A fragment of the corresponding murine genomic
DNA was also cloned, partially sequenced, and the positions of the cloned intron/exon boundaries were determined. Comparisons of the murine
scavenger receptors' sequences with the bovine, rabbit, and human sequences were used to refine a multidomain model of these trimeric, fibrous, membrane receptors. Metabolic labeling/immunoprecipitation experiments showed that most of the
macrophage scavenger receptor protein expressed by P388D1 cells was the N-glycosylated type II receptor; only small amounts of type I receptor were detected. Analysis of the binding properties of the receptors provided evidence that such differential expression of the type I and type II forms may have functional significance. There were substantial receptor-type (I
vs. II), as well as receptor-species (bovine vs. murine), differences in the inhibition of 125I-labeled
AcLDL (
acetylated low density lipoprotein) binding by
ReLPS, a form of bacterial
endotoxin. These differences arose, in part, because these receptors exhibited both high (Kd1(4 degrees C) = 0.05-0.2 micrograms
protein/ml) and low (Kd2(4 degrees C) = 2.5-12.8 micrograms
protein/ml) affinity binding of 125I-labeled
AcLDL. The ability of
ReLPS (1 mg/ml) to inhibit either or both of these two classes of binding interactions varied depending on the species and type of receptor.