title: Ligand responses of Vfr, the virulence factor regulator from Pseudomonas aeruginosa.
abstract: Vfr, a transcription factor homologous to the Escherichia coli cyclic AMP (cAMP) receptor protein (CRP), regulates many aspects of virulence in Pseudomonas aeruginosa. Vfr, like CRP, binds to cAMP and then recognizes its target DNA and activates transcription. Here we report that Vfr has important functional differences from CRP in terms of ligand sensing and response. First, Vfr has a significantly higher cAMP affinity than does CRP, which might explain the mysteriously unidirectional functional complementation between the two proteins (S. E. H. West et al., J. Bacteriol. 176:7532-7542, 1994). Second, Vfr is activated by both cAMP and cGMP, while CRP is specific to cAMP. Mutagenic analyses show that Thr133 (analogous to Ser128 of CRP) is the key residue for both of these distinct Vfr properties. On the other hand, substitutions that cause cAMP-independent activity in Vfr are similar to those seen in CRP, suggesting that a common cAMP activation mechanism is present. In the course of these analyses, we found a remarkable class of Vfr variants that have completely reversed the regulatory logic of the protein: they are active in DNA binding without cAMP and are strongly inhibited by cAMP. The physiological impact of Vfr's ligand sensing and response is discussed, as is a plausible basis for the fundamental change in protein allostery in the novel group of Vfr variants.
authors.affiliation: Department of Bacteriology, University of Wisconsin - Madison, Madison, Wisconsin 53706, USA.
authors.forename: Jose
authors.initials: J
authors.lastname: Serate
authors.forename: Gary P
authors.initials: GP
authors.lastname: Roberts
authors.forename: Otto
authors.initials: O
authors.lastname: Berg
authors.forename: Hwan
authors.initials: H
authors.lastname: Youn
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism*; D002373:Cyclic AMP Receptor Protein / Q000235:genetics / Q000378:metabolism*; D006152:Cyclic GMP / Q000378:metabolism*; D004252:DNA Mutational Analysis; D015964:Gene Expression Regulation, Bacterial; D007700:Kinetics; D011485:Protein Binding; D011550:Pseudomonas aeruginosa / Q000235:genetics / Q000502:physiology*; D037521:Virulence Factors / Q000096:biosynthesis
chemical_list: D001426:Bacterial Proteins; D002373:Cyclic AMP Receptor Protein; C091090:Vfr protein, Pseudomonas aeruginosa; D037521:Virulence Factors; D000242:Cyclic AMP; D006152:Cyclic GMP