Penicillin binding proteins (PBPs) have been extensively studied due to their importance to the physiology of bacterial cell wall
peptidoglycan and as targets of the most widely used class of
antibiotics, the β-
lactams. The existing paradigm asserts that PBPs catalyze the final step of
peptidoglycan biosynthesis, and β-
lactams inhibit their activities. According to this paradigm, a distinct
enzyme class, β-lactamases, exists to inactivate β-
lactams. This paradigm has been the basis for how
bacterial diseases are treated with β-
lactams. We tested whether this historical view accurately reflects the relationship between β-
lactams and the PBPs and the β-lactamase, BlaC, of Mycobacterium tuberculosis. BlaC was the major inactivator of the
cephalosporin subclass of β-
lactams. However, the PBPs PonA1 and PonA2 inactivated
penicillins and
carbapenems more effectively than BlaC. These findings demonstrate that select M.
tuberculosis PBPs are effective at inactivating several β-
lactams. Lesser-known PBPs, DacB, DacB1, DacB2, and Rv2864c, a putative PBP, were comparably more resistant to inhibition by all β-
lactam subclasses. Additionally, Rv1730c exhibited low affinity to most β-
lactams. Based on these findings, we conclude that in M.
tuberculosis, BlaC is not the only source of inactivation of β-
lactams. Therefore, the historical paradigm does not accurately describe the relationship between β-
lactams and M.
tuberculosis. IMPORTANCE M.
tuberculosis, the causative agent of
tuberculosis, kills more humans than any other bacterium. β-
lactams are the most widely used class of
antibiotics to treat
bacterial infections. Unlike in the historical model that describes the relationship between β-
lactams and M.
tuberculosis, we find that M.
tuberculosis penicillin binding proteins are able to inactivate select β-
lactams with high efficiency.