Beta-lactam is a common element of a group of antibiotics so-called beta-lactam antibiotics such as penicillins, cephamycins, and carbapennems. Beta-lactamses, produced by some bacteria, are responsible for the resistance to these antibiotics. The beta-lactamase from Y. pestis is a monomer, the overall structure is similar to those of other class C beta-lactamse and all catalytic residues are also in the similar locations in the conserved active site. Lactamase breaks down a beta-lactam by opening the four-atom ring. The protein was co-crystallized in the presence of Ala-Ala, however, citrate molecule which was not included in the crystallization, was found in the active site.