Mutation of Amino Acids 39–44 of Human CD14 Abrogates Binding of Lipopolysaccharide and Escherichia coli

Abstract

As a key receptor for lipopolysaccharide (LPS) on the surface of monocytes and macrophages, the CD14 molecule is primarily involved in non-specific host defense mechanisms against gram-negative bacteria. To delineate the structural basis of LPS binding, 23 mutants in the N-terminal 252 amino acids of human CD14 were generated and stably transfected into CHO cells. In each mutant, a block of five amino acids was substituted by alanine. Reactivity of the mutants with anti-CD14 mAbs, and their ability to interact with LPS and Escherichia coli were tested. 4 of 21 expressed CD14 mutants, ([Ala9–Ala13]CD14, [Ala39–Ala41, Ala43, Ala44]CD14, [Ala51–Ala55]CD14 and [Ala57, Ala59, Ala61–Ala63]CD14), are not recognized by anti-CD14 mAbs that interfere with the binding of LPS to human monocytes. However, only [Ala39–Ala41, Ala43, Ala44lCD14 is unable to react with fluorescein-isothiocyanate-labeled LPS or with FITC-labeled E. coli (055:B5). In addition, [Ala39–Ala4t. Ala43, Ala44]CD14 does not mediate LPS (E. coli 055:B5; 10 ng/ml)-induced translocation of nuclear factor κB in CHO-cell transfectants. The results indicate that the region between amino acids 39 and 44 forms an essential part of the LPS-binding site of human CD14.