In vitro potentiation of carbapenems with tannic acid against carbapenemase-producing enterobacteriaceae: exploring natural products as potential carbapenemase inhibitors.

AIMS: We hypothesized and confirmed that tannic acid (TA) reverses carbapenem resistance by inhibiting carbapenemases in class A and B carbapenemase-producing Enterobacteriaceae. METHODS AND RESULTS: Minimum inhibitory concentrations of carbapenems in the presence and absence of TA and other efflux pump inhibitors, TA-carbapenemases inhibition assays and computational studies showed that TA had the greatest effect on metallo-ß-lactamases (MBLs) followed by class A serine-ß-lactamases (SBLs). TA completely reversed the MICs of MBL producers from between 32 and ≥512 mg l-1 to susceptible values (<4 mg l-1 ) while substantially reducing the MICs of SBLs from between 16 and >512 mg l-1 to <4 to 16 mg l-1 . Tolerable cytotoxic effect was observed for the concentrations tested (8-1024 mg l-1 ). TA inhibited enzymes with a marked difference of ≈50% inhibition (IC50 ) for NDM-1 (270 µmol l-1 ) and KPC-2 (15  µmol l-1 ). CONCLUSION: TA inhibited both MBLs and SBLs by targeting their hydrophobic sites. Moreover, TA had a stronger binding affinity for MBLs than SBLs as the MBLs, specifically VIM-1 (-43·7220 ± 0·4513 kcal mol-1 ) and NDM-1(-44·2329 ± 0·3806 kcal mol-1 ), interact with a larger number of their catalytic active-site residues than that of OXA-48 (-22·5275 ±  0·1300 kcal mol-1 ) and KPC-2 (-22·1164 ± 0·0111 kcal mol-1 ). SIGNIFICANCE AND IMPACT OF THE STUDY: Tannic acid or its analogues could be developed into carbapenemase-inhibiting adjuvants to restore carbapenem activity in CRE infections, save many lives and reduce healthcare associated costs.

A comparative molecular dynamics study on BACE1 and BACE2 flap flexibility.

Beta-amyloid precursor protein cleavage enzyme1 (BACE1) and beta-amyloid precursor protein cleavage enzyme2 (BACE2), members of aspartyl protease family, are close homologs and have high similarity in their protein crystal structures. However, their enzymatic properties are different, which leads to different clinical outcomes. In this study, we performed sequence analysis and all-atom molecular dynamic (MD) simulations for both enzymes in their ligand-free states in order to compare their dynamical flap behaviors. This is to enhance our understanding of the relationship between sequence, structure and the dynamics of this protein family. Sequence analysis shows that in BACE1 and BACE2, most of the ligand-binding sites are conserved, indicative of their enzymatic property as aspartyl protease members. The other conserved residues are more or less unsystematically localized throughout the structure. Herein, we proposed and applied different combined parameters to define the asymmetric flap motion; the distance, d1, between the flap tip and the flexible region; the dihedral angle, φ, to account for the twisting motion and the TriCα angle, θ2 and θ1. All four combined parameters were found to appropriately define the observed "twisting" motion during the flaps different conformational states. Additional analysis of the parameters indicated that the flaps can exist in an ensemble of conformations, i.e. closed, semi-open and open conformations for both systems. However, the behavior of the flap tips during simulations is different between BACE1 and BACE2. The BACE1 active site cavity is more spacious as compared to that of BACE2. The analysis of 10S loop and 113S loop showed a similar trend to that of flaps, with the BACE1 loops being more flexible and less stable than those of BACE2. We believe that the results, methods and perspectives highlighted in this report would assist researchers in the discovery of BACE inhibitors as potential Alzheimer's disease therapies.