Characterization of the Binding of Apolipophorin Iii to Lipopolysaccharides

CHARACTERIZATION OF THE BINDING OF APOLIPOPHORIN III TO LIPOPOLYSACCHARIDES By Merve Oztug August, 2009 Apolipophorin III (apoLp-III) is a small insect apolipoprotein used as a model. Apolipoproteins neutralize lipopolysaccharides but the details are poorly understood. Lipopolysaccharides of gram negative bacteria can induce a septic shock, a common lethal condition. In the present study, the apoLp-III binding interaction with lipopolysaccharides from a variety of bacterial species was investigated using FPLC, dynamic light scatter, tyrosine fluorescence and native PAGE. ApoLp-III binding to Escherichia coli lipopolysaccharides resulted in the formation of complexes with a molecular mass of 400 kDa, a diameter of 18.7 nm, with 4 apoLp-III and 24 LPS molecules. The complexes with Klebsiella pneumoniae LPS were somewhat smaller. Analysis with truncated and detoxified lipopolysaccharides indicated that apoLp-III preferably binds to lipid A, while the O-antigen repeat elicited a weaker binding interaction. These findings led to a new model of apolipoprotein-lipopolysaccharide interaction and may be used for development of new therapeutic approaches to treat sepsis.