Urea-dependent virulence in uropathogenic bacteria

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DESCRIPTION(provided by applicant: Urease, which catalyzes the hydrolysis of urea to ammonia and carbonic acid is produced by diverse bacterial species including various aerobes, facultative anaerobes and obligate anaerohes Both Gram-negative and Gram-positive organisms are urease producers, as are species of mycobacteria and ureaplasma. Urease plays a significant role in virulence when expressed by urinary tract, oral, and gastroduodenal pathogens. Providencia stuartii and Proteus inirabilis, the two most common ureolytic uropathogens, express urcase only in the presence of urea. This urea-dependent expression is mediated by UreR, a transcriptional activator belonging to the AraCfamily of regulators. Evidence suggests that urea interacts directly with UreR, and thus is the effector molecule for this activator. Urea is Found at concentrations up to 500 mM in the urinary tract, a concentration that is at least 50 fold higher than that observed at other sites in the body. Thus for these uropathogens, urea is a signal molecule, and UreR is acting as a signal receptor, alerting the organism that it is in the urinary tract. UreR bound to urea is active as an transcriptional activator and has a high affinity for DNA. UreR not bound to urea is not active and has a low affinity for the I)NA binding site. Studies in this proposal are to examine the urea-UreR interaction and to determine the conformational changes associated with urea binding that result in active UreR. Two models are proposed, one in which UrcR forms a dimer, and the other in which UreR is active as a monomer. Studies are proposed to prove one of these models. The crucial urca-UreR interaction is examined in Aim #1, and the urea-UreR-DNA interaction in Aim #2. Aim #3 is to determine the X-ray structure of UreR, UreR bound to urea, and UreR bound to urea and the DNA binding site. Structures of mutant forms of UreR will also be generated. This work will elucidate the molecular mechanisms of this important regulator of a urovirulence, as well as extend our knowledge on the AraC-fainily of transcriptional activators.