||This thesis describes the structural and biochemical characterization of the β-lactamase BlaC from Mycobacterium tuberculosis (Mtb), and the Alr and YlmE proteins from Streptomyces coelicolor A3(2).Mtb is the main cause of tuberculosis. The inherent production of BlaC by Mtb makes the antibiotic treatment of tuberculosis particularly difficult because BlaC renders Mtb naturally resistant to β-lactam antibiotics. One possible way to circumvent this BlaC-mediated resistance is the co-administration of β-lactamase inhibitors, thus preventing antibiotics’ hydrolysis. The crystal structure of BlaC was determined in complex with the β-lactamase inhibitors clavulanic acid, sulbactam, tazobactam, and avibactam, and new BlaC-inhibitors covalent adducts were visualized. The affinity of BlaC for the inhibitors was further studied using catalytically inactive mutants of the enzyme.In parallel, the Alr and YlmE proteins from S. coelicolor A3(2) were studied. Alr and YlmE are putatively involved in the racemization of L-Ala into D-Ala. The latter is an essential peptidoglycan building block, and ensures cell wall compaction and bacterial survival. The structural and biochemical characterization of the heterologous, purified Alr and YlmE proteins showed that while Alr is indeed involved in Ala racemization, YlmE is not. Our findings revealed a possible new, surprising role for YlmE in nucleic acid binding.