Insight into the catalytic hydrolysis mechanism of New Delhi metallo-β-lactamase to aztreonam by molecular modeling

The monobactam antibiotic, aztreonam, can be hydrolyzed by some β-lactamases (NDM-1), whereas other β-lactamases, including VIM-1, have no hydrolytic activity on aztreonam. NDM-1 and VIM-1 are both metallo-β-lactamases (MBLs), but they catalyze hydrolysis at different active site residues, which is reflected in their obvious activity difference with aztreonam. In this work, to explore the catalytic hydrolysis mechanism of MBLs at the atomic level, molecular dynamic simulations were performed for NDM-1-aztreonam and VIM-1-aztreonam complexes based on the molecular docking analysis. Molecular modeling revealed the binding of aztreonam to the active regions of NDM-1 and VIM-1. Residues Met67, Phe70, Asp124, Thr190, and His250 play key roles in the binding of aztreonam with NDM-1. His116, Asp118, Cys198, His201, and His240 are the critical residues for the binding of aztreonam with VIM-1. Interestingly, Asp124 displayed the strongest binding energy (ΔEtotal = −11.28 kcal/mol), which was nearly 10 times higher than that of the other residues in the NDM-1-aztreonam complex. A similar result was found for the binding of aztreonam with VIM-1, with Asp118 displaying the strongest binding energy (ΔEtotal = −2.95 kcal/mol). These results implicated aspartic acid as the critical active site in the catalytic hydrolysis pocket of NDM-1 and VIM-1. However, in the VIM-1-aztreonam complex, because of the strong π-π interaction between the thiazol ring group of aztreonam and the imidazole ring groups of His201 and His240, the binding energy obtained from Asp118 become significantly weaker than that of aztreonam with Asp124 of NDM-1. Analysis of the simulation trajectory indicated that the thiazol ring plane of aztreonam is almost parallel to the imidazole ring planes of His201 and His240, implying that they can form a strong π-π interaction, which is consistent with the above results. On the basis of the computational biology results, it was confirmed that aspartic acid in the active pocket of NDM-1 and VIM-1 can effectively promote substrate hydrolysis, while histidine on the other side of the active pocket can block the binding of the substrate with aspartic acid, leading to the loss of hydrolysis.