Mimivirus TyrRS: preliminary structural and functional characterization of the first amino-acyl tRNA synthetase found in a virus

Abstract

The amoeba-infecting Mimivirus is the largest known double-stranded DNA virus, with a 400 nm particle size, comparable to that of mycoplasma. The complete sequence of its 1.2 Mbp genome has recently been determined [Raoult et al. (2004), Science, 306, 1344-1350] and revealed numerous genes that were not expected to be found in a virus, such as genes encoding translation components, including 4-amino-acyl tRNA synthetases and homologues to various translation initiation, elongation and termination factors. A comprehensive structural and functional study of these Mimivirus gene products was initiated, as they may hold important clues about the origin of DNA viruses. Here, the first preliminary crystallographic and functional results obtained on one of these targets, Mimivirus TyrRS, are reported. Preliminary phasing was obtained using an original combination of homology modelling and normal mode analysis. Experimental evidence that Mimivirus tyrosyl tRNA synthetase recombinant gene product does indeed activate tyrosine is also presented.

Figure 1

Enzymatic activity of mimivirus TyrRS versus E. coli TyrRS.

Figure 2

Multiple alignment of the mimivirus TyrRS sequence with structural homologues and related archeal and eukaryotic sequences. j1u and n3l correspond to the PDB structures (Kobayashi et al., 2003 ▶) and (Yang et al., 2002 ▶). The accession numbers of the homologous sequences are as follow: Ehisto, Entamoeba histolytica unfinished genome (gnl|TIGR_5759, ENTER63TR); Osati, Oryza sativa putative TyrRS (Q84PX0); Atha1, Arabidopsis thaliana putative TyrsRS (Q8S9J2); Atha2, Arabidopsis thaliana putative TyrsRS (P93018); Tobac, Nicotiana tabacum putative TyrRS (P93363); Pyoeli, Plasmodium yoelii putative TyrRS (Q7RH02); CParvum, Cryptosporidium parvum putative TyrRS(Q7YYA0). Black triangles correspond to residues known to be involved in interaction with the tyrosine, green triangles correspond to residues known to be involved in interaction with the acceptor and red stars correspond to residues known to be involved in interaction with the anticodon. The multiple alignment was generated using the T-COFFEE software (Poirot et al., 2004 ▶) in order to combine structural and sequence information and was used through the CaspR procedure to generate homology-based models of the mimivirus structure.