TcPDE4, a novel membrane-associated cAMP-specific phosphodiesterase from Trypanosoma cruzi.

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.