Swapping Interface Contacts in the Homodimeric tRNA‐Guanine Transglycosylase: An Option for Functional Regulation. Issue 32 (16th July 2018) - Ehrmann, Frederik Rainer
Abstract: The enzyme tRNA‐guanine transglycosylase, a target to fight Shigellosis, recognizes tRNA only as a homodimer and performs full nucleobase exchange at the wobble position. Active‐site inhibitors block the enzyme function by competitively replacing tRNA. In solution, the wild‐type homodimer dissociates only marginally, whereas mutated variants show substantial monomerization in solution. Surprisingly, one inhibitor transforms the protein into a twisted state, whereby one monomer unit rotates by approximately 130°. In this altered geometry, the enzyme is no longer capable of binding and processing tRNA. Three sugar‐type inhibitors have been designed and synthesized, which bind to the protein in either the functionally competent or twisted inactive state. They crystallize with the enzyme side‐by‐side under identical conditions from the same crystallization well. Possibly, the twisted inactive form corresponds to a resting state of the enzyme, important for its functional regulation. Abstract : Defining competence : The enzyme tRNA‐guanine transglycosylase recognizes and processes tRNA only as a homodimer. Upon addition of1, the enzyme adopts a novel twisted state (right), which is unable to bind tRNA and is thus functionally incompetent. Ligands2 and3 were discovered that crystallize with the protein side‐by‐side from the same crystallization well and stabilize the functionally competent and the incompetent form, respectively.