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Characterization of the interaction of lipid A and lipopolysaccharide with human serum albumin: implications for an endotoxin carrier function for albumin

The Wellcome Trust Research Laboratory and The Department of Gastrointestinal Sciences, Christian Medical College Hospital, Vellore, Molecular Biophysics Unit, Indian Institute of Science, Bangalore, India

P. Balaram

The Wellcome Trust Research Laboratory and The Department of Gastrointestinal Sciences, Christian Medical College Hospital, Vellore, Molecular Biophysics Unit, Indian Institute of Science, Bangalore, India

V.I. Mathan

The Wellcome Trust Research Laboratory and The Department of Gastrointestinal Sciences, Christian Medical College Hospital, Vellore, Molecular Biophysics Unit, Indian Institute of Science, Bangalore, India

The interactions of lipid A and lipopolysaccharide (LPS) with human serum albumin (HSA) were examined using fluorescence methods. Lipid A binds HSA with a stoichiometry of 2:1 with dissociation constants of 1.0 µM and 6.0 µM for the high- and low-affinity interactions, respectively. Lipid A displaces HSA-bound dansylsarcosine competitively, but not HSA-bound warfarin, suggesting that domain III-A, and not domain 11-A, is a lipid A binding site. Domain I does not contribute a site for lipid A. Based on these data, and the structural similarity between subdomains III-A and III-B, it is proposed that these two regions of HSA represent the high- and low-affinity sites of interaction of lipid A. Whole LPS also binds HSA, displacing dansylsarcosine, and its lipid A moiety appears to be the interaction site. However, there are differences between LPS and free lipid A. Polymyxin B forms ternary complexes with LPS bound to HSA, suggesting that the regions on LPS recognized by HSA and polymyxin B are different. The observed affinity of lipid A for HSA and mass action effects due to its abundance in the circulation would imply a major LPS carrier function for HSA.

Journal of Endotoxin Research, Vol. 2, No. 2, 99-106 (1995)
DOI: 10.1177/096805199500200204


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