Interaction of recombinant rho A GTP‐binding proteins with photoexcited rhodopsin

Abstract
The small molecular mass GTP‐binding proteins rho A, B and C are targets for ADP‐ribosyltransferase activity of the botulinum exoenzyme C3. The possible interaction of recombinant rho A proteins expressed in E. coli with photoexcited rhodopsin was studied by reconstitution with bovine rod outer segment (ROS) membranes depleted of endogenous GTP‐binding proteins by treatment with urea. As reported for C3 substrates present in untreated ROS membranes, ADP‐ribosylation of recombinant rho A proteins, both normal and Val‐14 mutant, by C3 was inhibited when reconstituted with illuminated compared to dark‐adapted ROS membranes pretreated with urea. GDP reduced the light‐induced inhibition, while GTP[S] and light inhibited ADP‐ribosylation of rho A proteins in a synergistic manner.