Vol. 13, Issue 11, 3878-3889, November 2002

Identification and Characterization of Two Unusual cGMP-stimulated Phoshodiesterases in Dictyostelium

Leonard Bosgraaf, Henk Russcher, Helena Snippe, Sonya Bader, Joyce Wind, and Peter J.M. Van Haastert^*

Department of Biochemistry, University of Groningen, 9747 AG Groningen, The Netherlands

Recently, we recognized two genes, gbpA and gbpB, encoding putative cGMP-binding proteins with a Zn²⁺-hydrolase domain and two cyclic nucleotide binding domains. The Zn²⁺-hydrolase domains belong to the superfamily of -lactamases, also harboring a small family of class II phosphodiesterases from bacteria and lower eukaryotes. Gene inactivation and overexpression studies demonstrate that gbpA encodes the cGMP-stimulated cGMP-phosphodiesterase that was characterized biochemically previously and was shown to be involved in chemotaxis. cAMP neither activates nor is a substrate of GbpA. The gbpB gene is expressed mainly in the multicellular stage and seems to encode a dual specificity phosphodiesterase with preference for cAMP. The enzyme hydrolyses cAMP ~9-fold faster than cGMP and is activated by cAMP and cGMP with a K_A value of ~0.7 and 2.3 µM, respectively. Cells with a deletion of the gbpB gene have increased basal and receptor stimulated cAMP levels and are sporogeneous. We propose that GbpA and GbpB hydrolyze the substrate in the Zn²⁺-hydrolase domain, whereas the cyclic nucleotide binding domains mediate activation. The human cGMP-stimulated cAMP/cGMP phosphodiesterase has similar biochemical properties, but a completely different topology: hydrolysis takes place by a class I catalytic domain and GAF domains mediate cGMP activation.