Binding of a photoreactive pyrethroid to β subunit of GTP-binding proteins

Abstract

Visual cycle signal transduction components and purified bovine brain GTP-binding proteins (G-proteins) have been used to study the possibility that pyrethroids interact with signal-transducing G-proteins. A photoactivatable arylazide derivative of fenvalerate ([ 3H]decyanoazidofenvalerate or [ 3H]DeCAF) has been used to photoaffinity label proteins in homogenized bovine retina, rod outer segments (ROS), and purified transducin—the retinal signal transducing G-protein—as well as the βγ subunit of G-proteins purified from bovine brain. All displayed [ 3H]DeCAF labeling to a 36-kDa protein. GTPγS treatment of ROS displaced labeling from membrane-bound protein(s) to a soluble fraction. [ 3H]DeCAF labeling of 36-kDa proteins was specific and saturable and greatest specific activity was obtained with purified transducin or β subunit of bovine brain G-proteins. Purified [ 3H]DeCAF-labeled β subunit of transducin (T β) was identified by immunoprecipitation with antibodies directed against T β or a synthetic peptide from T β. Treatment of ROS membranes by DeCAF resulted in stimulation of release of α subunit of transducin, as measured by [ 32P]ADP-ribosylation. These data complement previously published results and indicate that pyrethroids bind to the β subunit of G-proteins and modify their interaction with the α subunit.