(A) Maximum likelihood phylogenetic tree showing relationships among eukaryotic GCNA, Wss1, Spartan, and bacterial SprT protease domains. GCNA, Wss1, and Spartan are present across eukarya, including the most primitive eukaryotes, except that Wss1 proteins have been lost in animals. Gray and black circles indicate nodes with bootstrap values greater than 600 and 900 (out of 1000), respectively. Tree is based on alignment of the protease domains and was created with PhyML. (B) Structural modeling of GCNA, Wss1, and Spartan protease domains places GCNA in the minigluzincin family of proteases along with Wss1 and Spartan. Pairwise protein structure comparison using FATCAT (Ye and Godzik, 2004) detected strong structural similarity, as evidenced by small root-mean-square deviations (RMSDs), which are measures of the average distance (in Angstroms) between the carbon atoms of the superimposed proteins. All structures were found to be significantly similar.