Below are the structures from D-Ala D-Ala ligase (makes important links in the bacterial cell wall), glutathion synthetase, and two different nucleotide binding domains from carbamoyl phospate synthetase.

Based on the structure these domains appear similar and now are generally believed to be homologous, but based on pair wise comparison or randomization no significant similarity can be detected in the primary sequence. (alpha helices red, beta sheets yellow, only the positions of the alpha carbons of the backbne are indicated).