Association of a Zn2 + containing metallo β-lactamase with the anticancer antibiotic mithramycin

• MTR forms a high affinity complex with Zn2 + containing E[MBL] from B. cereus.
• Formation of MTR/Zn/MBL ternary complex inhibits enzyme activity of E[MBL].
• MTR alters secondary and tertiary structures of the enzyme.
• MTR and/or its derivatives could help overcome the defense of drug-resistant bacteria.

Pathogenic bacteria that are resistant to β-lactam antibiotics mostly utilize serine β-lactamases to degrade the antibiotics. Current studies have shown that different subclasses of metallo β-lactamases (E[MBL]) are involved in the defense mechanism of drug resistant bacteria. Here we report that the Zn2 + containing subclass B1 E[MBL] from Bacillus cereus binds to a naturally occurring anti-cancer drug mithramycin (MTR). Spectroscopic (CD and fluorescence) and isothermal titration calorimetry studies show that MTR forms a high affinity complex with the Zn2 + ion containing E[MBL]. Abolished interaction of MTR with apo E[MBL] suggests that the formation of this high affinity complex occurs due to the potential of MTR to bind bivalent metal ions like Zn2 +. Furthermore, CD spectroscopy, dynamic light scattering and differential scanning calorimetry studies indicate that the strong association with sub-micromolar dissociation constant leads to an alteration in the enzyme conformation at both secondary and tertiary structural levels. The enzyme activity decreases as a consequence to this conformational disruption arising from the formation of a ternary complex involving MTR, catalytic Zn2 + and the enzyme. Our results suggest that the naturally occurring antibiotic MTR, a generic drug, has the potential as an E[MBL] inhibitor.

DNA binding anti-cancer antibiotic mithramycin interacts with metallo β-lactamase from Bacillus cereus and disrupts its structure at both, the secondary and tertiary levels. Active-site metal ions are an obligatory requirement for this interaction, which leads to reduced activity of the enzyme in vitro.Figure optionsDownload as PowerPoint slide