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

The crystal structure of E. coli asparagine synthetase has been determined by X-ray diffraction analysis at 2.5 A 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 activities would generally follow the recruitment of a protein catalyzing a similar chemical reaction.