CD14 employs hydrophilic regions to "capture" lipopolysaccharides

CD14 participates in the host innate inflammatory response to bacterial LPS obtained from Escherichia coli and other Gram-negative bacteria. Evidence from several laboratories suggests that different regions of the amino-term inal portion of the molecule may be involved in LPS binding. In this report a series of single-residue serine replacement and charge reversal mutation s were generated to further elucidate the mechanism by which this protein m ay bind a multitude of different LPS ligands, Single-residue CD14 mutation proteins were examined for their ability to bind LPS obtained from E. coli, Porphyromonas gingivalis, and Helicobacter pylori and facilitate the activ ation of E-selectin from human endothelial cells. In addition, the single-r esidue CD14 mutation proteins were employed to perform monoclonal epitope-m apping studies with three LPS-blocking Abs that bound tertiary epitopes, Ev idence that several different hydrophilic regions of the amino-terminal reg ion of CD14 are involved in LPS binding was obtained. Epitope-mapping studi es revealed that these hydrophilic regions are located on one side of the p rotein surface. These studies suggest that CD14 employs a charged surface i n a manor similar to the macrophage scavenger receptor to "capture" LPS lig ands and "present" them to other components of the innate host defense syst em.