New sensor protein for phosphate dissociation during bacterial mRNA translation

Abstract

The translation initiation process is an important checkpoint that assures the correct protein production. Within this phase, Initiation Factor IF2 plays an important role along all early and late steps of the process. During late reactions, IF2 enhances the joining of the 50S subunit to the 30S Initiation Complex (IC) and positions initiator tRNA in the 70S IC. Concomitantly, IF2 hydrolyses a GTP molecule which led to propose that the active hydrolysis of GTP stimulates both above events. However, recent mutagenic studies of IF2 showed that inhibiting its GTP hydrolytic activity does not compromise the overall translation initiation process. Moreover, biochemical studies indicate that the dissociation of inorganic phosphate (Pi) is a late event, prior to the release of IF2. These findings indicated that it is the dissociation of Pi that weakens the interaction of IF2 with the ribosome. However, the GTP hydrolysis reaction is energetically favorable and may actively drive factor release. To elucidate which of the above postulates describe more accurately IF2 dependent reactions, here we design, produce and test a novel recombinant fluorescent phosphate binding sensor that specifically binds nearby the exit point of Pi during protein translation. This protein chimeras could evidence whether the IF2 dissociation is catalyzed by the Pi dissociation after GTP hydrolysis or by the reaction per se. Furthermore, the system provides a novel platform to study and systematically screen for new antimicrobial compounds.