The effector protein ExoY secreted by Pseudomonas aeruginosa is a nucleotidyl cyclase with preference for GTP
© Voigt et al; licensee BioMed Central Ltd. 2011
Published: 1 August 2011
Pseudomonas aeruginosa is an important opportunistic pathogen causing serious pulmonary, urogenital and systemic infections. P. aeruginosa injects four effector proteins into host cells via the type III secretion system. ExoY is one of these proteins.
ExoY was originally classified as adenylyl cyclase with homology to the typical calmodulin-stimulated adenylyl cyclase exotoxins CyaA from Bordetella pertussis and edema factor from Bacillus anthracis, but the pathophysiologial function of ExoY has remained elusive [1, 2]. Recently, our group showed that CyaA and edema factor possess a rather broad base specifity (ATP >> CTP > UTP) [3, 4], raising the question of wether ExoY may also bind and metabolize nucleoside 5’- triphosphates other than ATP.
We determined cyclic nucleotide concentrations in cells transfected with ExoY plasmid or infected with P. aeruginosa with a highly sensitive HPLC-MS/MS method. Moreover, we determined the catalytic activity of purified ExoY.
Comparison of ExoY with CyaA and EF
Function as toxin
Cytosolic cofactor (mammalian cells and D. discoideum)
Substrate-specificity purified enzyme
GTP >> UTP ≥ ATP > CTP
ATP >> CTP > UTP > GTP
ATP >> CTP > UTP > GTP
Substrate-specificity intact cells
UTP ~ GTP > ATP > CTP
(except for B103 cells)
ATP >> CTP > UTP >>
ATP >> CTP >>
UTP and GTP(ineffective)
ExoY is a nucleotidyl cyclase with preference for GTP, and the substrate-specificity of ExoY is clearly different from that of CyaA and edema factor. Our data open the door for future studies aiming at the elucidation of the as yet unknown pathophysiological function of ExoY and which role cCMP, cGMP and cUMP play in this process.
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