FATTY ACYLATION OF 2 INTERNAL LYSINE RESIDUES REQUIRED FOR THE TOXIC ACTIVITY OF ESCHERICHIA-COLI HEMOLYSIN

Hemolysin of Escherichia coli is activated by fatty acylation of the p rotoxin, directed by the putative acyl transferase HlyC and by acyl ca rrier protein (ACP). Mass spectrometry and Edman degradation of proteo lytic products from mature toxin activated in vitro with tritium-label ed acylACP revealed two fatty-acylated internal lysine residues, lysin e 564 and lysine 690. Resistance of the acylation to chemical treatmen ts suggested that fatty acid was amide linked. Substitution of the two lysines confirmed that they were the only sites of acylation and show ed that although each was acylated in the absence of the other, both s ites were required for in vivo toxin activity.