CHARACTERIZATION AND SEQUENCING OF A RESPIRATORY BURST-INHIBITING ACID-PHOSPHATASE FROM FRANCISELLA-TULARENSIS

Acid phosphatases (Acp) of intracellular pathogens have recently been implicated as virulence factors that enhance intracellular survival th rough suppression of the respiratory burst. We describe here the ident ification, purification, characterization, and sequencing of a novel b urst-inhibiting acid phosphatase from the facultative intracellular ba cterium, Francisella tularensis. Similar to other the burst-inhibiting Acps, F. tularensis Acp (AcpA) is tartrate-resistant and has broad su bstrate specificity. The AcpA enzyme is unique, however, in that it is easily released from the bacterial cell in soluble form, is a basic e nzyme, suppresses the respiratory burst of not only fMet-Leu-Phe but a lso phorbol 12-myristate 13-acetate-stimulated neutrophils and does no t fit into any of the three currently recognized classes of acid phosp hatase. We also report the complete nucleotide sequence of the gene ac pA, encoding AcpA, and the deduced primary structure of its encoded po lypeptide. Comparative sequence analyses of AcpA is discussed. To our knowledge, this is the first report describing the cloning and sequenc ing of a burst-inhibiting acid phosphatase.