Abstract of the PDB Structure's related Publication:
Dihydrouridine (D) is one of the most widely conserved tRNA modifications. Dihydrouridine synthase (Dus) is responsible for introducing D modifications into RNA by the reduction of uridine. Recently, a unique substrate-recognition mechanism using a small adapter molecule has been proposed for Thermus thermophilus Dus (TthDusC). To acquire insight regarding its substrate-recognition mechanism, the crystal structure of DusC from Escherichia coli (EcoDusC) was determined at 2.1 Å resolution. EcoDusC was shown to be composed of two domains: an N-terminal catalytic domain and a C-terminal tRNA-binding domain. An L-shaped electron density surrounded by highly conserved residues was found in the active site, as observed for TthDus. Structure comparison with TthDus indicated that the N-terminal region has a similar structure, whereas the C-terminal domain has marked differences in its relative orientation to the N-terminal domain as well as in its own structure. These observations suggested that Dus proteins adopt a common substrate-recognition mechanism using an adapter molecule, whereas the manner of tRNA binding is diverse.
Dihydrouridine synthases are a conserved enzyme family that is encoded by the orthologous COG0042 gene family (Kasprzak et al. 2012 ). Dihydrouridine (D) is a post-transcriptionally modified pyrimidine nucleoside. D results from the reduction of C5,6-double bond of a uridine residue in RNA transcripts (Kasprzak et al. 2012 ) that brings to the addition of two hydrogen atoms C6 and C5. With the absence of the double bond, dihydrouridine is believed to decrease region stability, promoting dynamic motion and accommodating loop structure. D is generated post-transcriptionally by Dus enzymes and it is found in different positions of tRNAs. In E.coli, tRNA dihydrouridine synthase B synthase catalyzes the synthesis of 5,6-dihydro uridine (D) via the reduction of C5,6. It is responsible for half of the wild-cellular tRNA modifications (Bishop et al. 2002 ).DusB and DusC enzymes together introduce all D at positions 16, 17, 20, and 20a in all tRNAs, but it is not known which of them modifies which base and in which tRNA. FMN is the cofactor for the reduction reaction.