Fold: N-terminal nucleophile aminohydrolases (Ntn hydrolases)

4 layers: alpha/beta/beta/alpha; has an unusual sheet-to-sheet packing

Lineage:

1. Root: scop
2. Class: Alpha and beta proteins (a+b)
   Mainly antiparallel beta sheets (segregated alpha and beta regions)
3. Fold: N-terminal nucleophile aminohydrolases (Ntn hydrolases)
   4 layers: alpha/beta/beta/alpha; has an unusual sheet-to-sheet packing

Superfamilies:

1. N-terminal nucleophile aminohydrolases (Ntn hydrolases) (5)
   N-terminal residue provides two catalytic groups, nucleophile and proton donor
   1. Class II glutamine amidotransferases (4)
      has slightly different topology than other families do
   2. Penicillin acylase, catalytic domain (2)
   3. Penicillin V acylase (1)
   4. Proteasome subunits (6)
   5. (Glycosyl)asparaginase (2)