Structural basis for tRNA-dependent amidotransferase function

Abstract

Besides direct charging of tRNAs by aminoacyl-tRNA synthetases, indirect routes also ensure attachment of some amino acids onto tRNA. Such routes may explain how new amino acids entered into protein synthesis. In archaea and in most bacteria, tRNAGln is first misaminoacylated by glutamyl-tRNA synthetase. Glu-tRNAGln is then matured into Gln-tRNAGln by a tRNA-dependent amidotransferase. We report the structure of a tRNA-dependent amidotransferase - that of GatDE from Pyrococcus abyssi. The 3.0 Å resolution crystal structure shows a tetramer with two GatD molecules as the core and two GatE molecules at the periphery. The fold of GatE cannot be related to that of any tRNA binding enzyme. The ammonium donor site on GatD and the tRNA site on GatE are markedly distant. Comparison of GatD and L-asparaginase structures shows how the motion of a β hairpin region containing a crucial catalytic threonine may control the overall reaction cycle of GatDE. © 2005 Elsevier Ltd. All rights reserved.