Lineage for Family d.3.1.21: YiiX-like

1. Root: SCOP 1.75

2. Class d: Alpha and beta proteins (a+b) [53931] (376 folds)

3. Fold d.3: Cysteine proteinases [54000] (1 superfamily) consists of one alpha-helix and 4 strands of antiparallel beta-sheet and contains the catalytic triad Cys-His-Asn

4. Superfamily d.3.1: Cysteine proteinases [54001] (22 families) the constitute families differ by insertion into and circular permutation of the common catalytic core made of one alpha-helix and 3-strands of beta-sheet

5. Family d.3.1.21: YiiX-like [159855] (1 protein) Pfam PF06520; DUF1105; circularly permuted active site residues compare to papain