Morrison D F, Cunnick J M, Oppert B, Takemoto D J
Department of Biochemistry, Kansas State University, Manhattan 66506.
J Biol Chem. 1989 Jul 15;264(20):11671-81.
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.
有大量证据表明，环鸟苷酸磷酸二酯酶（PDEγ）的γ亚基是一种多功能蛋白，它可能直接与PDE的催化亚基（PDEαβ）和转导素的α亚基（Tα）相互作用（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）。为了确定多功能PDEγ与Tα之间的相互作用区域，并确定这种相互作用的意义，合成了与PDEγ各个区域相对应的肽段，并测试它们抑制Tα的GTP酶活性的能力。其中一种肽段，PDEγ - 3（牛氨基酸残基31 - 45），以450微摩尔的半数抑制浓度（I50）抑制Tα的GTP酶活性。发现该肽段（PDEγ - 3）通过诱导转导素与视杆外段膜结合以及改变GTP/GDP交换来抑制Tα的GTP酶活性。合成了PDEγ - 3的类似物，以确定PDEγ与Tα相互作用所需的PDEγ - 3区域的结构。这些研究结果表明，去除带正电荷的氨基酸或任何潜在的氢键形成氨基酸会增加抑制Tα的GTP酶活性的半数抑制浓度（I50）。疏水氨基酸的取代没有影响。这些结果表明，亲水相互作用可能对于PDEγ与Tα的结合以及PDEγ对Tα的GTP酶活性的抑制至关重要。观察到的PDEγ - 3对Tα和PDE的影响表明，PDEγ是一种多功能蛋白，它可能在视网膜转导级联反应的失活中发挥不止一种作用。
