Specific endotoxic lipopolysaccharide-binding proteins on murine splenocytes. II. Membrane localization and binding characteristics.

We have characterized the binding of LPS to an 80-kDa LPS-binding protein detected by an LPS photoaffinity probe to be present on murine splenocytes. Specific binding of LPS to the 80-kDa protein is directly proportional to LPS concentration at low concentrations of LPS and is saturable at high concentrations of LPS. Binding is inhibited by both homologous and heterologous underivatized LPS as well as by polysaccharide-free lipid A, indicating a specificity for the biologically active component of LPS. Analysis of the kinetics of binding indicate a time-dependent increase over the first 15 min, but increases are not detected after this time. Binding of LPS to the 80-kDa LPS-binding protein is reduced but still readily detectable at 4 degrees C in the presence of azide. The presence of the 80-kDa LPS-binding protein in an isolated cytoplasmic membrane fraction of murine splenocytes as well as its release from intact splenocytes by octylglucoside suggest that this LPS-binding protein is membrane localized. The results are consistent with, but do not establish unequivocally, the identity of the 80-kDa LPS-binding protein as a specific membrane receptor for lipid A.