Exploring β-lactam interactions with DacB1: unraveling optimal therapies for combating drug-resistant .

Abstract:

Tuberculosis (TB) continues to pose a global public health threat, exacerbated by rising drug-resistant strains of (Mtb). DacB1, a D,D-carboxypeptidase critical in Mtb peptidoglycan biosynthesis, is a promising target for β-lactam antibiotics (BLs), which remain underutilized in TB treatment. Dual BL therapy may enhance efficacy by inactivating multiple targets within the peptidoglyan synthesis pathway. Minimum inhibitory concentrations (MICs) for β-lactams and β-lactamase inhibitors against Mtb H37Ra, H37Rv, and clinical isolates showed that imipenem, meropenem, or tebipenem MICs were reduced when combined with amoxicillin or ceftriaxone or β-lactamase inhibitors such as clavulanate or durlobactam. Timed electrospray ionization mass spectrometry (ESI-MS) captured acyl-enzyme adducts between DacB1 and BLs, revealing binding interactions with carbapenems (imipenem, meropenem, and tebipenem) but not most penicillins or cephalosporins except cloxacillin and cefoxitin. Differential scanning fluorimetry (DSF) combined with circular dichroism (CD) confirmed physical and structural changes in DacB1 upon BL binding despite no alteration in melting temperature. Carbapenem-DacB1 interactions were notably faster with imipenem, likely due to reduced steric hindrance compared to meropenem and tebipenem. Molecular modeling revealed conserved penicillin-binding protein motifs within the active site of DacB1: SXXK124, S176XN178, and K282TG284 (PDB ID # 4PPR). Building on this, molecular docking suggested favorable interactions between these motifs and the carbapenems: the carbapenem carbonyl group aids in positioning within DacB1’s oxyanion hole, ready for acylation, while hydrophobic interactions with the cyclic R2 side chains and C1 methyl groups in meropenem and tebipenem contribute to steric hindrance hence slow acyl-enzyme formation. These findings enhance our understanding of DacB1 inhibition and suggest that carbapenems, particularly in combination therapies, hold promise as effective TB treatments.