TARGET-CELL SPECIFICITY OF THE PASTEURELLA-HAEMOLYTICA LEUKOTOXIN IS UNAFFECTED BY THE NATURE OF THE FATTY-ACYL GROUP USED TO ACTIVATE THE TOXIN IN-VITRO

The leukotoxin (LktA) of Pasteurella haemolytica is active only agains t cells of ruminant origin. It is synthesised as an inactive protoxin encoded by the lktA gene and post-translationally modified to the acti ve toxin by the product of the lktC gene. The LktA and LktC proteins w ere expressed separately in Escherichia coli and partially purified. A ctive LktA was produced in vitro in the presence of LktC and acyl-acyl carrier protein (ACP) charged separately in vitro with a fatty-acyl g roup. The toxic activity and target cell specificity of LktA and adeny late cyclase toxin (CyaA), a toxin active against a wide variety of ma mmalian cells, were investigated after activation with ACP charged wit h different fatty acids. Palmitoyl-ACP produced the most active toxin in both cases and, although other fatty acids were also effective, the fatty acid preference was the same for the in vitro activation of bot h toxins. Activated LktA remained ruminant cell-specific whichever acy l group was used to acylate the A protoxin. (C) 1998 Federation of Eur opean Microbiological Societies. Published by Elsevier Science B.V. Al l rights reserved.