Beta-lactamase, class-C active site <p>This active site signature detects all class C Beta-lactamases. The class C beta-lactamases are serine hydrolases belonging to MEROPS peptidase family S12 (D-Ala-D-Ala carboxypeptidase B family, clan SE). They are classed as non-peptidase homologues.</p><p>Beta-lactamases (<db_xref db="EC" dbkey="3.5.2.6"/>) [<cite idref="PUB00004510"/>, <cite idref="PUB00003800"/>] are enzymes which catalyse the hydrolysis of an amide bond in the beta-lactam ring of antibiotics belonging to the penicillin/cephalosporin family. Four kinds of beta-lactamase have been identified [<cite idref="PUB00000133"/>]. Class-B enzymes are zinc containing proteins whilst class -A, C and D enzymes are serine hydrolases. The three classes of serine beta-lactamases are evolutionary related and belong to a superfamily [<cite idref="PUB00000464"/>] that also includes DD-peptidases and a variety of other penicillin-binding proteins (PBP's). All these proteins contain a Ser-x-x-Lys motif, where the serine is the active site residue. Although clearly homologous, the sequences of the three classes of serine beta-lactamases exhibit a large degree of variability and only a small number of residues are conserved in addition to the catalytic serine.</p>