Identification and characterization of a novel family of cyclic nucleotide phosphodiesterases

We report the cloning, expression, and characterization of a new family of cyclic nucleotide phosphodiesterase (PDE) that has unique kinetic and inhibitor specificities. A clone corresponding to the C terminus of this PDE was initially identified by a bioinformatic approach and used to isolate a cDNA that is likely full-length. This novel PDE, designated as MMPDE9A1, shows highest mRNA expression in kidney with lower levels in liver, lung, and brain. The mRNA size by Northern blot analysis is approximately 2.0 kilobases, and the cDNA encoding PDE9A1 is 1929 base pairs in length. The largest open reading frame predicts a protein of 534 amino acids with a molecular mass of 62,000 Da. When expressed in COS-7 cells, PDE9A1 activity was not inhibited well by either the nonselective inhibitor 3-isobutyl-1-methyl-xanthine or the new selective PDE5 inhibitor, sildenafil, but it is inhibited by the PDE1/5 inhibitor (+)-cis-5,6a, 7,8,9 hyl] phenylmethyl]-5-methyl-cylopent[4,5]imidao[2, 1-b]purin-49(3H)one (SCH51866) with an IC50 of 1.55 microM. This new phosphodiesterase is highly specific for cGMP. Its Km of approximately 0.07 microM for cGMP is the lowest yet reported for a PDE, being at least 40-170 times lower than that of PDE5 and PDE6, respectively.