Lipopolysaccharide and peptidoglycan share binding sites on human peripheral blood monocytes

p73, a binding site for lipopolysaccharide (LPS) on human peripheral blood monocytes was identified using the radiolabeled photoaffinity cross-linker sulfosuccinimidyl 2-(p-azidosalicylamido)ethyl-1,3'-dithiopropionate (SASD). The 125I-labeled conjugate of SASD and LPS (125I-labeled ASD-LPS) was bound to monocytes and UV cross-linked, and the cellular extracts were analyzed with two-dimensional SDS-PAGE and autoradiography. In addition to the major binding site on human monocytes at 73 kDa, isoelectric point 5.95, there were multiple minor binding sites that recognized both smooth and rough LPS. Binding of 125I-labeled ASD-LPS to monocytes is concentration dependent, decreased in the absence of calcium and magnesium, and inhibited by either excess LPS or the low-molecular-weight soluble isolate of bacterial cell wall peptidoglycan (sPGN). However, sPGN only minimally stimulates tumor necrosis factor (TNF) secretion by human peripheral blood mononuclear cells. In contrast, the relatively insoluble high-molecular-weight peptidoglycan significantly stimulates TNF secretion.