Significance The location of the active site of enzymes with the same fold is invariably conserved. The β-propeller fold exemplifies this feature with all functions located at what is termed their anterior surface. Herein, however, we show that the active site of a glycoside hydrolase that adopts the β-propeller fold is located to the posterior surface of the α- l -rhamnosidase. The enzyme also displays a catalytic apparatus that utilizes a single histidine instead of the canonical pair of carboxylate residues deployed by the vast majority of glycoside hydrolases. The capacity to engineer catalytic functionality into the posterior surface of other family members provides insight into the evolution of this enzyme family.