Pig Liver Esterase (PLE) as Biocatalyst in Organic Synthesis: From Nature to Cloning and to Practical Applications

Pig liver esterase (PLE, EC 3.1.1.1) has been employed extensively for research purposes during the last three decades, especially in kinetic resolutions, in desymmetrizations of prochiral substrates, and in the synthesis of nucleosides. Its practical use, however, has been traditionally hampered for several reasons. The existence of several isoenzymes with different (enantio)selectivities has caused problems in reproducibility when different PLEs have been used for a certain reaction. In addition, being an animal-derived­ enzyme, its use in several fields, such as pharmaceuticals, is excluded, as the enzyme could act as a source of viral transmission. To overcome these drawbacks - and thus make this powerful enzyme useful for organic chemists - many efforts have been devoted to cloning and over-expressing PLE in some heterologous hosts, thus assuring the recombinant production of (pure) PLE. After solving some technical problems, this has recently been achieved, when successful cloning of isoenzyme γ from PLE (γ-rPLE) in E. coli at high productivities was reported. This important achievement re-establishes­ the potential use of this enzyme as a biocatalyst in organic (asymmetric) synthesis. Furthermore, it also opens the possibility of developing new recombinant PLEs - through biological strategies - leading to new PLEs with better (novel) applications than those reported­ for wild-type PLEs.