β-lactamases (EC 3.5.2.6) [1,2] are enzymes which catalyze the hydrolysis of an amide bond in the β-lactam ring of antibiotics belonging to the penicillin/cephalosporin family. Four kinds of β-lactamase have been identified [2]. Class-B enzymes are zinc containing proteins whilst class -A, C and D enzymes are serine hydrolases. Class-B β-lactamases have been described in several Gram-negative bacterial species; they seem to share the characteristic of being able to hydrolyze carbapenem compounds which are new β-lactam antibiotics of great therapeutic potential.

There are a number of conserved regions in the sequence of known class-B β-lactamases [3]. Most of them are centered on residues known [4] to be involved in binding the zinc ion essential for the enzyme's catalytic activity. We designed two signature patterns for this class of enzyme. The first contains three residues involved in binding zinc ions. The second pattern contains a cysteine which is also a zinc ligand.