Table 2.
β-Lactam | Experimentally measuredb |
S conformer |
I conformer |
|||||
---|---|---|---|---|---|---|---|---|
Km (μM) | kcat/Km (s−1 μM−1) | Lowest binding energy (kcal/mol) | Estimated Ki (nM) | Population (%) | Lowest binding energy (kcal/mol) | Estimated Ki (nM) | Population (%) | |
Ampicillin | 22 | 2.2 | −12.07 | 1.4 | 89 | −11.74 | 2.5 | 11 |
Penicillin G | 16 | 3.0 | −12.35 | 0.9 | 79 | −12.53 | 0.7 | 21 |
Piperacillin | 12 | −12.70 | 0.5 | 97 | −11.56 | 3.4 | 3 | |
Cefepime | 77 | −11.29 | 5.3 | 83 | −12.18 | 1.2 | 17 | |
Cefotaxime | 10 | −12.04 | 1.5 | 71 | −14.23 | 0.04 | 29 | |
Cefoxitin | 49 | −10.61 | 16.7 | 51 | −12.32 | 0.9 | 26 | |
−12.58c | 0.6c | 4c | −11.10d | 7.3d | 11d | |||
−13.46e | 0.1e | 8e | ||||||
Ceftazidime | 181 | −11.02 | 8.4 | 8 | −12.7 | 0.5 | 86 | |
−11.25d | 5.7d | 6d | ||||||
Cefuroxime | 8 | −12.06 | 1.4 | 45 | −12.57 | 0.6 | 55 | |
Cephalothin | 10 | −11.90 | 1.9 | 35 | −14.30 | 0.03 | 62 | |
−12.02d | 1.5d | 3d | ||||||
Faropenem | −12.11 | 1.3 | 14 | −12.76 | 0.4 | 74 | ||
−11.96d | 1.7d | 12d | ||||||
Imipenem | 94 | 4.3 | −10.39 | 24.2 | 62 | −11.31 | 5.2 | 17 |
−10.18c | 34.4c | 7c | −10.79d | 12.2d | 14d | |||
Meropenem | 49 | 2.6 | −10.64 | 15.8 | 84 | −11.65 | 2.9 | 5 |
−11.59c | 3.2c | 11c | ||||||
Clavulanic acid | Not detected | −11.44 | 4.1 | 100 | ||||
Aztreonam | Not detected | −12.84 | 0.4 | 93 | ||||
−12.38e | 0.8e | 7e | ||||||
Sulbactam | −10.79 | 4.7 | 17 | −11.61 | 3.1 | 57 | ||
−11.55d | 3.4d | 26d | ||||||
Moxalactam | −10.97 | 9.1 | 1 | |||||
−15.12f | 0.008f | 99f |
In the S conformer, the amide oxygen of the β-lactams interacts with Zn1, while the carboxylic group coordinates with Zn2. The I conformer has the carboxylic or sulfate oxygens interacting with Zn1 and Zn2.
The Km and kcat/Km values are taken from the papers by Yong et al. (38) and by Thomas et al. (28), respectively.
The S2 conformer has switched interactions with the zinc ions from the S conformer.
The I2 conformer has the orientation of the carboxylic group opposite that of I1.
In the I3 conformer, the bridging hydroxide/water is displaced by the carboxylic or sulfate oxygen.
In the I4 conformer, the tyrosyl-carboxylic group chelates with the zinc ions.