Substrate Deacylation Mechanism of Serine beta-lactamases

The substrate deacylation mechanisms of serine-β-lactamases (classes A, C and D) wereinvestigated by theoretical calculations. The deacylation of class A proceeds via fourelementary reactions. The rate-determining process is the tetrahedral intermediate (TI)formation and the activation energy is 24.6 kcal/mol at the DFT level. The deacylation doesnot proceed only by Glu166, which acts as a general base, but Lys73 also participates in thereaction. The C3-carboxyl group of the substrate reduces the barrier height at the TIformation (substrate-assisted catalysis). In the case of class C, the deacylation consists of twoelementary processes. The activation energy of the TI formation has been estimated to be30.5 kcal/mol. Tyr150Oη is stabilized in the deprotonated state in the acyl-enzyme complexand works as a general base. This situation can exist due to the interaction with twopositively charged side chains of lysine (Lys67 and Lys315). The deacylation of class D alsoconsists of two elementary reaction processes. The activation energy of the TI formation is ca.30 kcal/mol. It is thought that the side chain of Lys70 is deprotonated and acts as a generalbase. When Lys70 is carbamylated, the activation energy is reduced to less than 20 kcal/mol.This suggests that the high hydrolysis activity of class D with carbamylated Lys70 is due tothe reduction of activation energy for deacylation. From these results, it is concluded that thecontribution of the lysine residue adjacent to the serine residue is indispensable for theenzymatic reactions by serine-β-lactamases.

https://opac.ll.chiba-u.jp/da/curator/900023223/

https://opac.ll.chiba-u.jp/da/curator/900023223/manuscript_BPB.pdf

学術雑誌論文

0918-6158

AA10885497

Biological and Pharmaceutical Bulletin

29

11

2151

2159

2006-11-01

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