Molecular architecture and ligand recognition determinants for T4 RNA ligase

Abstract

RNA ligase type 1 from bacteriophage T4 (Rnl1) is involved in countering a host defense mechanism by repairing 5′-PO4 and 3′-OH groups in tRNALys. Rnl1 is widely used as a reagent in molecular biology. Although many structures for DNA ligases are available, only fragments of RNA ligases such as Rnl2 are known. We report the first crystal structure of a complete RNA ligase, Rnl1, in complex with adenosine 5′-(α,β- methylenetriphosphate) (AMPcPP). The N-terminal domain is related to the equivalent region of DNA ligases and Rnl2 and binds AMPcPP but with further interactions from the additional N-terminal 70 amino acids in Rnl1 (via Tyr 37 and Arg54) and the C-terminal domain (Gly269 and Asp272). The active site contains two metal ions, consistent with the two-magnesium ion catalytic mechanism. The C-terminal domain represents a new all α-helical fold and has a charge distribution and architecture for helix-nucleic acid groove interaction compatible with tRNA binding.