A Comparative Study of 2′,3′‐Cyclic‐Nucleotide 3′‐Phosphodiesterase in Vertebrates: cDNA Cloning and Amino Acid Sequences for Chicken and Bullfrog Enzymes

In mammalian brain, two 2',3'-cyclic-nucleotide 3'-phosphodiesterase (EC 3.1.4.37) isoforms, CNP1 and CNP2, are translated, respectively, from the two mRNAs, which have been transcribed and processed by alternative use of the two transcription start points and by differential splicing. In the present study, the cDNAs encoding chicken CNP2 and bullfrog CNP1, respectively, were isolated, and the amino acid sequences of chicken CNP2 and bullfrog CNP1 were deduced. Western blot analysis showed that chicken brain contains a major CNP2-type protein together with a minor unidentified isoform, and bullfrog brain contains only a CNP1-type protein. All available amino acid sequences of vertebrate 2',3'-cyclic-nucleotide 3'-phosphodiesterases were aligned and compared. Three conserved motif sequences were noted: (a) an ATP-binding site near the amino terminus, (b) an isoprenylation site at the carboxyl terminus, and (c) a probable catalytic site resembling the active site of beta-ketoacyl synthase (EC 2.3.1.41). The second and the third motifs are conserved also in goldfish RICH (regeneration-induced 2',3'-cyclic-nucleotide 3'-phosphodiesterase homologue), which has been shown recently to have 2',3'-cyclic-nucleotide 3'-phosphodiesterase activity. The third motif (probably catalytic site) was assigned for the first time in the present report.