Role of lipopolysaccharide on the structure and function of Ą-hemolysin from Escherichia coli

V. HERLAX; L. BAKAS

Buenos Aires, Argentina

Congreso; IUPAB XIV; 2002

IUPAB ( International Union for Pure and Applied Biophysics)

     Alpha hemolysin is a protein toxin secreted by some pathogenic strains of Escherichia coli. Previous studies suggest a connection between HlyA and lipopolysaccharide (LPS). LPS might be required for the maximal production of some RTX toxins and might be a cofactor in some of the biological effects of them  It is a unique component of the outer membrane of all gram-negative bacteria forming an impermeable barrier in addition to imparting strong hydrophilicity to the surface. This molecule has amphiphatic properties and consists of a hydrophobic fatty-acyl-containing lipid A; a highly charged and hydrophilic core containing KDO linked to phosphate and ethanolamine; and a polar uncharged hydrophilic repeating polysaccharide containing an O-specific chain. LPS readily interacts with numerous biomolecules including phospholipids, membranes and serum proteins.  We have studied the role of LPS on the staility and function of this toxin. The HlyA conformation in both LPS-free an LPS- bound form was studies by tryptophan fluorescence and their denaturation by temperature and guanidine HCl indicating that the stability is incresed by the presence of LPS.These results are confirmed by a higher papain digestion susceptibility. On the other hand, the presence of negative and polar residues on the LPS, reduces the tendence of HlyA to self- aggregation.These results suggest that HlyA structure modification by LPS could be involve in changes of the tertiary or quaternary structure.HlyA and LPS combine by hydrophobic interaction to form an active toxin whose stability is aided by the LPS.