STRUCTURAL AND PHYSICOCHEMICAL CHARACTERISTICS OF BORDETELLA-PERTUSSIS ADENYLATE KINASE, A TRYPTOPHAN-CONTAINING ENZYME

The adk gene from the Gram-negative pathogen Bordetella pertussis was cloned by complementing the thermosensitive Escherichia coli adk strai n CR341T28. B. pertussis adenylate kinase is a 218-amino-acid protein that has high similarity with adenylate kinase from Escherichia coli a nd Hemophilus influenzae (57%). A distinct characteristic of enzyme fr om B. pertussis, not found in other bacterial adenylate kinases, is th e presence of a tryptophan residue at position 185. Although distant f rom the catalytic site, this single tryptophan serves as a convenient probe for monitoring the binding of nucleotide substrates or analogs t o the enzyme. Differential scanning calorimetry and equilibrium unfold ing experiments in guanidine . HCI indicate similar stabilities for ad enylate kinase from B. pertussis and E. coli. An extensive comparison between physico-chemical properties of adenylate kinase from B. pertus sis and the enzyme from E. coli showed that the kinetic and structural properties of the two enzymes are very similar. However, infrared spe ctroscopy has allowed to identify small but significant differences in the secondary structure of the two proteins.