Tyrosine fluorescence analysis of apolipophorin III-lipopolysaccharide interaction.
Apolipophorin III (apoLp-III) is an exchangeable apolipoprotein that binds to lipopolysaccharides (LPS). Polyacrylamide gel electrophoresis analysis demonstrated that apoLp-III from Galleria mellonella associated with various truncated LPS variants, including lipid A. Subsequent binding studies were performed employing the intrinsic tyrosine fluorescence properties of apoLp-III, which is highly quenched in the unbound state. A marked increase in tyrosine fluorescence intensity was observed upon binding to LPS or detoxified LPS, indicating a new microenvironment for Tyr-142. This also implies that the LPS carbohydrate region is involved in LPS binding. Dissociation constants (Kd) measured by apoLp-III titration were estimated at approximately 1 microM. Increasing the ionic strength did not decrease the Kd, neither did LPS phosphate removal. In addition, truncation apoLp-III mutants, lacking two complete helices, were still able to associate with LPS. This indicates that the association of apoLp-III with LPS may not be governed by charge but by hydrophobic interactions.
Leon
Leonardo J
LJ
Department of Chemistry and Biochemistry, California State University Long Beach, Long Beach, CA 90840, USA.
Pratt
Cindy C
CC
Vasquez
Lesley J
LJ
Weers
Paul M M
PM
D000818:Animals; D001053:Apolipoproteins / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D005453:Fluorescence; D006863:Hydrogen-Ion Concentration; D057927:Hydrophobic and Hydrophilic Interactions; D007700:Kinetics; D007915:Lepidoptera / Q000737:chemistry*; D008070:Lipopolysaccharides / Q000378:metabolism*; D017433:Protein Structure, Secondary; D013050:Spectrometry, Fluorescence; D014443:Tyrosine / Q000737:chemistry*
D001053:Apolipoproteins; D008070:Lipopolysaccharides; C042470:apolipophorin III; D014443:Tyrosine