Site-directed mutagenesis of the cGMP phosphodiesterase gamma subunit from bovine rod outer segments: role of separate amino acid residues in the interaction with catalytic subunits and transducin alpha subunit.

The recombinant and 21 mutant phosphodiesterase (PDE) gamma subunit (PDE gamma) genes were expressed by sequential transcription and translation in vitro. Inhibitory properties of these mutants and their interactions with PDE catalytic and transducin alpha subunits were studied. The interaction of the PDE gamma subunit with the catalytic ones proceeds in two steps--primary binding and inhibition. The central region of the PDE gamma molecule enriched with the basic amino acid residues (particularly, Lys-29, Lys-31 and Arg-33), is involved in the primary binding, and the PDE gamma C-terminus plays the key role in inhibition. The spatial orientation of the C-terminus is of great importance here. The PDE gamma C-terminus also affects binding to catalytic moieties.