An interface of interaction between photoreceptor cGMP phosphodiesterase catalytic subunits and inhibitory gamma subunits.
Cyclic guanosine 5'-monophosphate (cGMP) phosphodiesterase (PDE) regulates the level of cGMP on transduction of a visual signal in vertebrate photoreceptor cells. Two identical inhibitory PDE gamma subunits (Pgammas) block catalytic activity of PDE-alpha and -beta subunits (Palphabeta) in the dark. The primary regions of Pgamma involved in the interaction with Palphabeta are a central polycationic region, Pgamma-24-45, and a C-terminal region of Pgamma. Recently, we have shown that the C-terminal region of Pgamma, which is the major Pgamma inhibitory domain, blocks PDE activity by binding to the catalytic site of PDE (Artemyev, N. O., Natochin, M., Busman, M., Schey, K. L., and Hamm, H. E. (1996) Proc. Natl. Acad. Sci. U. S. A. 93, 5407-5412). Here, we localize the site on the rod cGMP PDE alpha subunit that binds to the central polycationic domain of Pgamma. This site is located within a region that links a second noncatalytic cGMP binding site with the catalytic domain of PDE. A polypeptide coresponding to this region, Palpha-461-553, expressed as a glutathione S-transferase fusion protein in Escherichia coli and isolated after cleavage of the fusion protein with thrombin, blocks inhibition of PDE activity by Pgamma. In addition, Palpha-461-553 binds to the Pgamma-24-45 region (Kd, 7 microM), as measured by a fluorescent increase in a Pgamma-24-45Cys peptide labeled with 3-(bromoacetyl)-7-diethylaminocoumarin. The Palpha-461-553 region was further characterized by using a set of synthetic peptides. A peptide corresponding to residues 517-541 of Palpha (Palpha-517-541) effectively suppressed inhibition of PDE activity by Pgamma and bound to Pgamma-24-45Cys labeled with 3-(bromoacetyl)-7-diethylaminocoumarin (Kd, 22 microM). Palpha-517-541 also competes with the activated rod G-protein alpha-subunit for binding to Pgamma labeled with lucifer yellow vinyl sulfone. This suggests that light activation of rod PDE by the G-protein transducin involves competition between transducin alpha-guanosine 5'-triphosphate and Palpha-517-541 for binding to the Pgamma-24-45 region. Based on the results, we propose a linear model of interactions between catalytic and inhibitory PDE subunits.
Natochin
M
M
Department of Physiology and Biophysics, University of Iowa College of Medicine, Iowa City, Iowa 52242, USA.
Artemyev
N O
NO
D015106:3',5'-Cyclic-GMP Phosphodiesterases / Q000737:chemistry* / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002417:Cattle; D003001:Cloning, Molecular; D004789:Enzyme Activation; D019204:GTP-Binding Proteins / Q000737:chemistry*; D008969:Molecular Sequence Data; D010786:Photoreceptor Cells / Q000737:chemistry*; D011485:Protein Binding; D012374:Rod Cell Outer Segment / Q000737:chemistry*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014785:Vision, Ocular
D015106:3',5'-Cyclic-GMP Phosphodiesterases; D019204:GTP-Binding Proteins