Abstract

β-lactam antibiotics (i.e. penicillin) are crucial to the field of medicine. Yet due to the reliance and over-prescription of these antibiotics, bacteria become resistant to many drugs that were once extremely efficient. Many resistant bacteria express an enzyme, known as a β-lactamase, which hydrolyzes the amide bond of the defining four membered β-lactam ring, rendering the drug inactive. The carbapenem-hydrolyzing class D β-lactamases (CHDLs), are a particularly worrisome subtype of the class D enzymes. OXA-24 is a clinically relevant member of the CHDLs and, therefore, is a key target to inhibit. Atomic structures of OXA-24 in complexes with β-lactam ligands would inform inhibitor design efforts. Currently OXA-24 is crystallized using high concentrations of ammonium sulfate (2.0 M), resulting in the presence of a sulfate ion in the active site of the enzyme, preventing certain ligands from binding. In order to discover an inhibitor for OXA-24, a complex without the ammonium sulfate in the active site must be found. In this experiment, we show that the lowest concentration that still allows for crystallization of OXA-24 is 1.4 M ammonium sulfate. We also discovered a novel crystallization condition for OXA-24 with a significantly lower concentration of sulfate (0.2 M lithium sulfate). Optimizing this new condition may aid in future crystallization efforts and eventual inhibitor discovery.