AS enzymes catalyse the hydrolysis of amide bonds (CO-NH2), although the family has diverged widely with regard to substrate specificity and function.
Nonetheless, these enzymes maintain a core alpha/beta/alpha structure, where the topologies of the N- and C-terminal halves are similar.
AS enzymes characteristically have a highly conserved C-terminal region rich in serine and glycine residues, but devoid of aspartic acid and histidine residues, therefore they differ from classical serine hydrolases.
These enzymes possess a unique, highly conserved Ser-Ser-Lys catalytic triad used for amide hydrolysis, although the catalytic mechanism for acyl-enzyme intermediate formation can differ between enzymes.
[1] Examples of AS signature-containing enzymes include: As of late 2018, 162 structures have been solved for this family, which can be accessed at the Pfam Archived 2021-09-18 at the Wayback Machine.