Antiendotoxin agents share molecular homology within their lipopolysaccharide binding domains

Background. The purpose of this study was to determine whether antiendotoxi n agents exhibit molecular homology within their lipopolysaccharide (LPS) b inding domains, suggesting a common mechanism of action. We hypothesized th at the presence of positively charged basic amino acids or a paucity of neg atively charged acidic amino acids, or both, would be a critical characteri stic of that portion of the molecule that binds to the highly negatively ch arged deep core/lipid A (DCLA) region of LPS. Materials and methods. We analyzed the amino acid sequences of the variable light (V-L) and heavy (V-H) chain complementarity-determining regions (CDR s) of anti-DCLA monoclonal antibodies(mAbs) 1B6, 5A5, and 7C5 and compared them with (1) the GDRs of three irrelevant control mAbs and (2) the LPS bin ding region of bactericidal permeability-increasing protein (BPI). We purif ied and amplified the specific nucleotide sequences of the variable regions using reverse transcriptase polymerase chain reaction. DNA was sequenced b y dideoxy termination, and protein sequences were deduced and analyzed. The percentages of acidic, basic, polar, and hydrophobic amino acids within V- H and V-L chain CDRs were determined. Results. We identified a paucity of negatively charged acidic amino acids e xclusively within V-L chain CDRs of anti-DCLA mAbs(P < 0.005). Although inc reased, the number of positively charged basic residues was not statistical ly significantly different; neither was the number of polar or hydrophobic amino acids. Conclusions. Our data suggest that the near absence of negatively charged a cidic residues is critical for LPS binding. This characteristic appears to reside exclusively in the V-L chain CDRs of anti-DCLA mAbs, (C) 1999 Academ ic Press.