Interaction of the gamma-subunit of retinal rod outer segment phosphodiesterase with transducin. Use of synthetic peptides as functional probes.
There is considerable evidence which suggests that the gamma-subunit of cGMP phosphodiesterase (PDE gamma) is a multifunctional protein which may interact directly with both the catalytic subunits of PDE (PDE alpha beta) and the alpha-subunit of transducin (T alpha) (Whalen, M., and Bitensky, M. (1989) Biochem. J. 259, 13-19; Griswold-Prenner, I., Young, J. H., Yamane, H. K., and Fung, B. K.-K. (1988) Invest. Ophthalmol. & Visual Sci. 29, (Suppl.) 218). To determine the region of interaction between the multifunctional PDE gamma and T alpha, and to determine the significance of this interaction, peptides corresponding to various regions of PDE gamma were synthesized and tested for their ability to inhibit the GTPase activity of T alpha. One of these peptides, PDE gamma-3 (bovine amino acid residues 31-45), inhibited the GTPase activity of T alpha with an I50 of 450 microM. The peptide (PDE gamma-3) was found to inhibit the GTPase activity of T alpha by inducing the binding of transducin to the rod outer segment membrane and by altering the GTP/GDP exchange. Analogs of PDE gamma-3 were synthesized to determine the required structure of the PDE gamma-3 region needed for the interaction of PDE gamma with T alpha. The results of these studies indicated that the removal of the positively charged amino acids or any of the potential hydrogen-bonding amino acids increased the I50 for the inhibition of the GTPase activity of T alpha Substitution of the hydrophobic amino acids had no effect. These results indicate the hydrophilic interactions may be essential for the binding of PDE gamma to T alpha and for the inhibition of the GTPase activity of T alpha by PDE gamma. The observed effects of PDE gamma-3 on T alpha and on PDE suggest that PDE gamma is a multifunctional protein which may play more than one role in the deactivation of the retinal transduction cascade.
Morrison
D F
DF
Department of Biochemistry, Kansas State University, Manhattan 66506.
Cunnick
J M
JM
Oppert
B
B
Takemoto
D J
DJ
D015106:3',5'-Cyclic-GMP Phosphodiesterases / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D001667:Binding, Competitive; D002417:Cattle; D002942:Circular Dichroism; D020558:GTP Phosphohydrolases / Q000037:antagonists & inhibitors; D008969:Molecular Sequence Data; D010455:Peptides / Q000138:chemical synthesis / Q000378:metabolism; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism*; D010786:Photoreceptor Cells / Q000201:enzymology*; D011863:Radioimmunoassay; D012374:Rod Cell Outer Segment / Q000201:enzymology*; D015293:Transducin / Q000494:pharmacology*
D010455:Peptides; D010727:Phosphoric Diester Hydrolases; D015106:3',5'-Cyclic-GMP Phosphodiesterases; D020558:GTP Phosphohydrolases; D015293:Transducin