[Binding of porin with lipopolysaccharide from Yersinia pseudotuberculosis]

Interactions, of porin a protein from Yersinia pseudotuberculosis, with S- and R-LPS and lipid A were investigated by means of fluorescence and CD-spectroscopy, differential scanning microcalorimetry and CsCl gradient ultracentrifugation. S-LPS--porin monomer stoichiometry was shown by fluorescence titration to be 6:1. Ultracentrifugation data suggest that the maximum number of LPS molecules bound per porin monomer in three. Two equivalent lipid A binding sites on porin were determined, data the associated binding constant being 6.1 x 10(4) M-1. Interactions between S- and R-LPS and porin monomer were shown to by positive and negative cooperativity, respectively. The data suggest an important role of the structural moieties of LPS molecule in the binding process. On the basis of these results and the structure of ligands a mechanism of LPS-porin interaction is discussed.