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TcPDE4, a novel membrane-associated cAMP-specific phosphodiesterase from Trypanosoma cruzi
Guillermo D Alonso1, Alejandra C Schoijet, Héctor N Torres
1Instituto de Investigaciones en Ingeniería Genética y Biología Molecular, Consejo Nacional de Investigaciones Científicas y Técnicas, Universidad de Buenos Aires, Argentina. galonso@dna.uba.ar
Abstract:
Cyclic nucleotide phosphodiesterases constitute the only known mechanism to inactivate regulatory signals involving cAMP or cGMP. In our laboratory a cAMP-specific phosphodiesterase associated to the flagellar apparatus, named TcPDE1, was identified in Trypanosoma cruzi. By using the catalytic domain sequence of TcPDE1 to screen a Trypanosoma cruzi genomic data base, a novel T. cruzi phosphodiesterase sequence was found and characterized. TcPDE4 encodes a 924-amino acid protein and shows homology with the PDE4 vertebrate subfamily. The sequence shows three conserved domains, FYVE, phosphohydrolase and PDEaseI. The FYVE zinc-finger domain is characteristic of proteins recruited to phosphatidylinosytol 3-phosphate-containing membranes, whereas the two others are characteristic of phosphohydrolases and members of the cyclic nucleotide phosphodiesterases. Sequence analysis shows all characteristic domains present at the type-4 phosphodiesterases specific for cAMP. Moreover, TcPDE4 shows the inhibition profile characteristic for PDE4 subfamily, with an IC50 of 10.46 microM for rolipram and 1.3 microM for etazolate. TcPDE4 is able to complement a heat-shock-sensitive yeast mutant deficient in phosphodiesterase genes. The enzyme is specific for cAMP, Mg(2+)-dependent and its activity is not affected by cGMP or Ca(2+). The association of TcPDE4 with membranes was studied by subcellular fractionation of recombinant yeast and extraction in several conditions. Most of the enzyme remained associated to the membrane fraction after treatment with high salt concentration, detergent, or chaotropic agents. This support previous hypotheses that in this parasite cAMP phosphodiesterases, and consequently cAMP levels, are compartmentalized.
Insights
A novel cyclic nucleotide phosphodiesterase, TcPDE4, was identified in Trypanosoma cruzi. This enzyme specifically degrades cAMP and associates with cellular membranes, suggesting compartmentalized signaling in the parasite.
Area of Science:
- Parasitology
- Molecular Biology
- Biochemistry
Background:
- Cyclic nucleotide phosphodiesterases (PDEs) are crucial for regulating intracellular cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) signaling.
- The parasite Trypanosoma cruzi relies on PDEs for signal inactivation, with a previously identified cAMP-specific PDE (TcPDE1) associated with its flagellar apparatus.
Purpose of the Study:
- To identify and characterize novel phosphodiesterase genes in Trypanosoma cruzi.
- To investigate the enzymatic properties, substrate specificity, and cellular localization of the newly discovered PDE, TcPDE4.
Main Methods:
- Genomic database screening using the catalytic domain of TcPDE1.
- Sequence analysis to identify conserved domains (FYVE, phosphohydrolase, PDEaseI).
- Enzymatic assays to determine substrate specificity, cofactor dependency, and inhibition profiles (using rolipram and etazolate).
- Functional complementation of a phosphodiesterase-deficient yeast mutant.
- Subcellular fractionation and membrane association studies.
Main Results:
- A novel T. cruzi phosphodiesterase gene, TcPDE4, was identified, encoding a 924-amino acid protein with homology to the vertebrate PDE4 subfamily.
- TcPDE4 possesses characteristic domains (FYVE, phosphohydrolase, PDEaseI) and exhibits a PDE4-like inhibition profile (IC50 for rolipram: 10.46 µM; for etazolate: 1.3 µM).
- The enzyme specifically hydrolyzes cAMP, requires Mg(2+), and its activity is independent of cGMP or Ca(2+).
- TcPDE4 successfully complemented a yeast mutant lacking PDE activity.
- Subcellular fractionation revealed that TcPDE4 predominantly associates with cellular membranes, remaining membrane-bound even after treatments with high salt, detergents, or chaotropic agents.
Conclusions:
- TcPDE4 represents a novel cAMP-specific phosphodiesterase in Trypanosoma cruzi, belonging to the PDE4 subfamily.
- Its membrane association supports the hypothesis of compartmentalized cAMP signaling pathways within the parasite.
- Understanding TcPDE4 function is critical for elucidating parasite physiology and potentially developing new therapeutic strategies.
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