Enantioselective Resolution of γ-Lactam by a Novel Thermostable Type II (+)-γ-Lactamase from the Hyperthermophilic Archaeon Aeropyrum pernix

Abstract

A thermostable formamidase from the aerobic hyperthermophilic archaeon Aeropyrum pernix was revealed a novel type II (+)-γ-lactamase. This type II (+)-γ-lactamase is only composed of 377 amino acid residues, in contrast to another thermostable (+)-γ-lactamase from Sulfolobus solfataricus with 504 amino acid residues (type I). It is interesting that there are low identities between these two (+)-γ-lactamases, and herein, we further proved that at least two types of (+)-γ-lactamases exist in nature due to enzyme promiscuity. The gene of this thermostable (+)-γ-lactamase was cloned, functionally expressed in Escherichia coli BL21, and purified by a simple yet effective heat treatment method. It showed incredible thermostability, retaining 100 % of its activity after 12 h at 100 °C. The optimum temperature for this enzyme was supposed to be more than 100 °C, and the optimum pH for this enzyme was about 9.0. The lactamase maintained its activity in the presence of most metal ions, except for Cu²⁺. This thermo- and alkaline-tolerant (+)-γ-lactamase presents promising properties for the industrial application. Specifically, it could be used for the production of chirally pure (−)-γ-lactam for the synthesis of well-known carbocyclic nucleosides like abacavir and peramivir. The optical purity of the chiral product reached over 97 % enantiomeric excess.