Lipopolysaccharide (LPS) binding to 73-kDa and 38-kDa surface proteins on lymphoreticular cells: preferential inhibition of LPS binding to the former by Rhodopseudomonas sphaeroides lipid A.

Using a photoactivable, radioiodinated lipopolysaccharide probe, [125I]ASD-LPS (derivatized from purified E. coli 0111:B4 S-LPS), we earlier reported the presence of a 73-kDa (p73) predominant LPS-binding protein on mouse lymphocytes and macrophages with specificity for the lipid A region of LPS. Both Re-LPS from Salmonella minnesota and purified lipid A will inhibit the binding of LPS to the p73 LPS receptor. In the studies reported here, we have found that non-toxic diphosphoryl lipid A purified from Rhodo-pseudomonas sphaeroides has the capability to inhibit the binding of [125I]ASD-LPS to the p73 protein. However, using the same LPS probe and photoaffinity cross-linking techniques, our data suggest that a less dominant 38-kDa (p38) LPS-specific binding protein identified on mouse splenocytes, J774.1 macrophage-like cell line, and 70Z/3 pre B-cell line by SDS-PAGE is not inhibited by purified lipid A, even at a concentration in 50-fold excess of that of [125]ASD-LPS. The binding of the LPS probe to the 38 protein could be inhibited in a dose-dependent manner by underivatized native S. minnesota Re-LPS (composed only of Kdo and lipid A). We speculate that this p38 LPS-binding protein may manifest a specificity for inner core oligosaccharide determinants on LPS.