INTERACTION OF PORIN WITH LIPOPOLYSACCHAR IDE FROM YERSINIA-PSEUDOTUBERCULOSIS

Interactions, of porin a protein from Yersinia pseudotuberculosis, wit h S- and R-LPS and lipid A were investigated by means of fluorescence and CD-spectroscopy, differential scanning microcalorimetry and CsCl g radient ultracentrifugation. S-LPS - porin monomer stoichiometry was s hown by fluorescence titration to be 6:1. Ultracentrifugation data sug gest that the maximum number of LPS molecules bound per porin monomer in three. Two equivalent lipid A binding sites on porin were determine d, data the associated binding constant being 6.1 x 10(4) M(-1). Inter actions between S- and R-LPS and porin monomer were shown to by positi ve and negative cooperativity, respectively, The data suggest an impor tant role of the structural moieties of LPS molecule in the binding pr ocess. On he basis of these results and the structure of ligands a mec hanism of LPS-porin interaction is discussed.