Phosphocholine: A new receptor for E.coli alpha hemolysin

R. VAZQUEZ; S.MATÉ; L.BAKÁS; V. HERLAX

Salta

Congreso; 3 er Latin American Protein Society Meeting; 2010

SAB y LAPS

á-hemolysin (HlyA) is an exotoxin secreted by some pathogenic strains of E.coli that causes lysis of several mammalian cells. Although the toxin causes the lysis of liposome composed of pure lipids, some studies demonstrated the presence of receptors for the toxin in several target cells. In a previous work we have demonstrated that HlyA oligomerizases on membrane microdomains which are enriched in sphingomyelin and cholesterol. Taking into account that some toxins, like leukocidin of S. aureus, binds to  phosphocholine, the aim of this work was to study phosphocholine as receptor of alpha hemolysin, so as to  explain why the toxin lyses pure liposomes as well as erythrocytes that lack glycophorin, as sheep and rabbit erythrocytes. For this purpose we studied the hemolytic activity of the toxin using horse, sheep and rabbit erythrocytes. Lysis inhibition by phosphocholine was done, demonstrating that hemolysis was inhibited in the three species but this inhibition was more notorious in sheep erythrocytes. The analysis of the lipid composition of the three membranes by HPTLC, demonstrated that the three species present differences in the amount of sphingomyelin and phosphatidylcholine. Considering that a tryptophan is involved in the binding of leukocidin to phosphocholine, we studied the fluorescence spectra of HlyA and four protein mutants where one of the four tryptophan of HlyA is replaced. The results demonstrated that phosphocholine, as polar group of sphingomyelin, is receptor of HlyA, and the possible tryptophan involved in this binding is W 579.