Abstract
Lipopolysaccharide dispersed in the blood by Gram-negative bacteria can be a potent inducer of septic shock. One research focus has been based on antibody sequestration of lipid A (the endotoxic principle of LPS); however, none have been successfully developed into a clinical treatment. Comparison of a panel of anti-lipid A antibodies reveals highly specific antibodies produced through distinct germ line precursors. The structures of antigen-binding fragments for two homologous mAbs specific for lipid A, S55-3 and S55-5, have been determined both in complex with lipid A disaccharide backbone and unliganded. These high resolution structures reveal a conserved positively charged pocket formed within the complementarity determining region H2 loops that binds the terminal phosphates of lipid A. Significantly, this motif occurs in unrelated antibodies where it mediates binding to negatively charged moieties through a range of epitopes, including phosphorylated peptides used in diagnostics and therapeutics. S55-3 and S55-5 have combining sites distinct from anti-lipid A antibodies previously described (as a result of their separate germ line origin), which are nevertheless complementary both in shape and charge to the antigen. S55-3 and S55-5 display similar avidity toward lipid A despite possessing a number of different amino acid residues in their combining sites. Binding of lipid A occurs independent of the acyl chains, although the GlcN-O6 attachment point for the core oligosaccharide is buried in the combining site, which explains their inability to recognize LPS. Despite their lack of therapeutic potential, the observed motif may have significant immunological implications as a tool for engineering recombinant antibodies.
Highlights
Bacterial Gram-positive and Gram-negative infections can lead to septic shock, with estimates as high as one million annual cases in the United States with a mortality rate as high as 50% [1,2,3]
We report binding data and crystal structures of unliganded and liganded antigen-binding fragments (Fabs) for lipid Abinding monoclonal antibodies (mAbs), S55-3 and S55-5, as a step toward the elucidation of the basis for specificity toward lipid A
Mouse Immunization and mAb Isolation—BALB/c mice were successfully immunized with BBP-bis-Gly-divinyl sulfone (DVS)-BSA as shown by the appearance of serum antibodies against the immunizing antigen
Summary
Bacterial Gram-positive and Gram-negative infections can lead to septic shock, with estimates as high as one million annual cases in the United States with a mortality rate as high as 50% [1,2,3]. The amphipathic lipopolysaccharide (LPS) responsible for Gram-negative-induced septic shock is normally shed from the bacterial outer membrane but can be released in great amounts upon cell death [4]. Antibodies specific for the various LPS components have been reported [15,16,17,18,19,20,21,22,23,24], the structural variation in the core and O-polysaccharide regions together with the rapid onset of septic shock have hindered their introduction into clinical use [4, 12, 25,26,27]. The search for monoclonal antibodies specific for lipid A did not produce any that would recognize the free LPS, it did produce a number of antibodies of different germ line
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
