COOPERATIVE PORIN-LIPOPOLYSACCHARIDE INTE RACTION

The interaction of the pore-forming protein (porin) from the outer mem brane of Yersinia pseudotuberculosis with the S- and R-forms of lipopo lysaccharide (LPS) from this bacterium was studied. Analysis of the eq uilibrium binding of I-125-labeled S- and R-LPS, as well as the compet itive inhibition of this reaction by lipid A, core oligosaccharide, an d O-specific polysaccharide, suggests that there are binding sites on the porin molecule specific to these fragments of the LPS molecule. Th e binding of R-LPS occurs at independent sites of two classes with K-a 1.7 x 10(5) and 1.1 x 10(5) M(-1). S-LPS interacts with porin with po sitive cooperation (h 1.6) and K-a 0.8 x 10(5) M(-1). The number of bi nding sites was found to be nine and four for R- and S-LPS, respective ly. Molecular mechanisms of the interaction are discussed.