”Some structural insights into the role of Apolipoprotein A-I on the neutralization of bacterial Lipopolysaccharide.”

HENNING, MARÍA FLORENCIA; BAKÁS, LAURA

Acapulco, México

Congreso; 2nd Latin American Protein Society Meeting; 2007

LAPSM

Lipopolysaccharide (LPS or endotoxin) is released from the outer surface membrane of Gram negative bacteria. LPS induces a variety of biological effects which could culminate in manifestations of septic shock. In vivo protection against endotoxin by plasma high density lipoprotein (HDL) was previously reported indicating that anti-endotoxin function of HDL was due to the interaction between LPS and apolipoproteína A-I (apoA-I), the major protein component of HDL. Effects of LPS-apoA-I interaction on the function of this protein were showed in the 1st LAPS Meeting. The aim of the present study was to investigate the interactions of LPS on the apoA-I structure.  A decrease in the intrinsic fluorescence intensity of apoA-I after LPS incubation was observed which can be explained if any protein conformational changes takes place resulting in a quenching of Trp  by neighbor residues.  CD spectra showed changes in the environment in the region of helices of apoA-I after LPS incubation. Chemical stability was measured after incubating apoA-I and apoA-I: LPS at various [GdnHCl].  ApoA-I unfolding curve reached a plateau, and a two-model state fits the experimental data. However, LPS diminishes the cooperativity of the unfolding. G H2O was 3544 kcal/mol and 1424 kcal/mol in the absence and presence of LPS respectively, and m (coefficient proportional to the amount of hydrophobic regions of the protein exposed to solvent when the protein unfolds) decrease from 2107 to 937 in the presence of LPS.  ApoA-I-LPS interaction was confirmed by photolabelling of apoAI   after reaction with    125I –LPS ASD derivative.