| Autor: |
Diaz, N., Suarez, D., Sordo, T. L., Merz, K. M., Jr. |
| Zdroj: |
The Journal of Physical Chemistry - Part B; November 2001, Vol. 105 Issue: 45 p11302-11313, 12p |
| Abstrakt: |
Herein we present results of a computational study on the benzylpenicillin acylation of the class A TEM1 β-lactamase via hydroxyl-only and hydroxyl and carboxylate assisted processes. These mechanisms correspond to a one-step Ser130-assisted process and a second route in which the β-lactam carboxylate and the Ser130 hydroxyl group help the proton transfer from the hydroxyl group of Ser70 to the β-lactam leaving N atom. The internal geometry of the reactive part of the TEM1-benzylpenicillin system is taken from a B3LYP/6-31+G* computational study on the methanol-assisted methanolysis reaction of a penicillin model compound (3α-carboxypenam). The 6-acylamino side chain and the 2-methyl groups of benzylpenicillin, together with the closer residues around the essential Ser70, are relaxed by carrying out geometry optimizations with a hybrid QM/MM method. The corresponding relative energies in the protein combine the B3LYP/6-31+G* electronic energies of the reactive subsystem with semiempirical PM3 energies of the TEM1-benzylpenicillin systems both in vacuo and in solution. The PM3 calculations on the TEM1-benzylpenicillin systems are performed with a Divide and Conquer linear-scaling method. The hydroxyl and carboxylate assisted pathway, which is the most favored one, is in agreement with the experimentally observed kinetic isotope effects and is also compatible with the effects of mutagenesis experiments on the Ser130 residue. These results suggest that a similar mechanism for the formation of acylenzyme intermediates could be relevant to other active-site serine penicillin-recognizing enzymes. |
| Databáze: |
Supplemental Index |
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