Structural domains comprising this superfamily share the structure of the metallo-beta-lactamase (MBL) domain which is found in several proteins which, besides beta-lactamases and metallo-beta-lactamases, include several other metalloenzymes such as alkyl sulphatase. The alkyl sulphatase SdsA1 is a representative of the metallo-beta-lactamase fold.

Enzymes containing this domain are mostly hydrolases. The metal-binding end, with the exception for the Zn2+-binding loops, is responsible for substrate recognition and, therefore, unique to each enzyme. The MBL fold is stable scaffold that has been used repeatedly during evolution to catalyze a diverse range of chemical reactions. Structurally, this diversity is achieved by varying the sequence and length of loops near the active site, which allows the accommodation of various substrates. Combination of the MBL domain with auxiliary substrate-, product- or cofactor-binding domains, have greatly extended the range of functions of proteins containing this domain PMID:16684886.