Molecular cloning of an immunogenic and acid-induced isocitrate dehydrogenase gene from Coxiella burnetii

The Coxiella burnetii icd gene encoding an immunogenic dimeric NADP(+)-depe ndent isocitrate dehydrognase (IDH) was cloned by screening a C. burnetii g enomic library with a human positive serum and sequenced. The predicted gen e product consists of 427 amino acids (M-r = 46 600) and showed high identi ty to the IDHs of Escherichia coli (74%), Salmonella enterica (73%) and IDH -I of Vibrio sp. (71%). The cloned gene complemented an icd-defective E. co li mutant producing a recombinant IDH that had the same biochemical propert ies as the enzyme from purified C.burnetii. Unlike the homologs from other bacteria, the cloned enzyme was expressed to the highest level in low pH co nditions. This distinct property of the cloned IDH suggests that C. burneti i icd gene may have a role in the adaptation of the organism to the harsh a cidic environment of the eucaryotic phagolysosomes. (C) 1999 Published by E lsevier Science B.V. All rights reserved.