Metallo-beta-lactamase protein fold

The metallo-beta-lactamase protein fold is a protein domain contained in class B beta-lactamases and a number of other proteins.
These proteins include thiolesterases, members of the glyoxalase II family, that catalyse the hydrolysis of S-D-lactoyl-glutathione to form glutathione and D-lactic acid and a competence protein that is essential for natural transformation in "Neisseria gonorrhoeae" and could be a transporter involved in DNA uptake. Except for the competence protein these proteins bind two zinc ions per molecule as cofactor.
Metallo-beta-lactamases are important enzymes because they are involved in the breakdown of antibiotics by antibiotic-resistant bacteria. It is unclear whether metallo-beta-lactamase activity evolved once or twice within the superfamily; if twice, this would suggest structural exaptation.