Crystal structure of asparagine synthetase reveals a close evolutionary relationship to class II aminoacyl-tRNA synthetase

The crystal structure off. coli asparagine synthetase has been determined by X-ray diffraction analysis at 2.5 Angstrom resolution. The overall structure of the enzyme is remarkably similar to that of the catalytic domain of yeast aspartyl-tRNA synthetase despite low sequence similarity. These enzymes have a common reaction mechanism that implies the formation of an aminoacyl-adenylate intermediate. The active site architecture and most of the catalytic residues are also conserved in both enzymes. These proteins have probably evolved from a common ancestor even though their sequence similarities are small. The functional and structural similarities of both enzymes suggest that new enzymatic activites would generally follow the recruitment of a protein catalyzing a similiar chemical reaction.