Crystal structure of sulfolobus tokodaii sua5 complexed with.

The hypermodified nucleoside N-threonylcarbamoyladenosine resides at position 37 of tRNA molecules bearing U at position 36 and maintains translational fidelity in the three kingdoms of life. The N-threonylcarbamoyl moiety is composed of -threonine and bicarbonate, and its synthesis was genetically shown to require YrdC/Sua5. YrdC/Sua5 binds to tRNA and ATP. In this study, we analyzed the -threonine-binding mode of Sua5 from the archaeon Sulfolobus tokodaii. Isothermal titration calorimetry measurements revealed that S. tokodaii Sua5 binds -threonine more strongly than -serine and glycine. The Kd values of Sua5 for -threonine and -serine are 9.3 μ M and 2.6 m M, respectively. We determined the crystal structure of S. tokodaii Sua5, complexed with AMPPNP and -threonine, at 1.8 Å resolution. The -threonine is bound next to AMPPNP in the same pocket of the N-terminal domain. Thr118 and two water molecules form hydrogen bonds with AMPPNP in a unique manner for adenine-specific recognition. The carboxyl group and the side-chain hydroxyl and methyl groups of -threonine are buried deep in the pocket, whereas the amino group faces AMPPNP. The -threonine is located in a suitable position to react together with ATP for the synthesis of N-threonylcarbamoyladenosine. Proteins 2011. © 2011 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]