Structural characteristics of human histidyltRNA synthetase

Aminoacyl-tRNA synthetase is an enzyme that recognizes its cognate amino acid and tRNA to catalyze the reaction of forming of aminoacyl-tRNAs. Histidyl-tRNA synthetase (HisRS) belongs to the class II family of amioacyl-tRNA synthetases and is responsible for the incorporation of histidine into proteins. To elucidate the structure, full-length human HisRS (hHisRS) was over-expressed, purified and crystallized. We determined the crystal structure to 2.8 Å resolutions by the molecular replacement. The space group was P41212 with a = b = 97.66 Å, c = 254.40 Å. α=90.00°, β=90.00°, γ=90.00°. Overall structure of human HisRS is quite similar to that of other HisRSs except the insertion domain in the catalytic domain of hHisRS (residues 214-290), which likely binds to tRNA. The N-terminal WHEP-TRS domain of hHisRS, which plays an important role in non-canonical function of HisRS, do not appear in this structure. While the anticodon binding and insertion domain showed structural diversity among the class II ARS sub-families, the catalytic domain showed substantial structural conservation in class II ARSs. Structural comparison with bacterial HisRSs and human ARSs identified that novel insertion domain and strictly conserved catalytic site residues for the interaction with ATP and histidine.