The Role of Enoyl Reductase in the Monacolin K Biosynthesis Pathway in Monascus spp.

Monacolin K (MK), a secondary metabolite produced by <i>Monascus</i> spp. with the ability to inhibit cholesterol production, is structurally identical to lovastatin produced by <i>Aspergillus terreus.</i> In the lovastatin biosynthetic pathway, the polyketide synthase (PKS) encoded by <i>lovB</i> must work together with the enoyl reductase encoded by <i>lovC</i> to ensure lovastatin production. However, it is unclear whether <i>mokA</i> and <i>mokE</i> in the MK gene cluster of <i>Monascus</i> spp., both of which are highly homologous to <i>lovB</i> and <i>lovC</i>, respectively, also have the same functions for MK biosynthesis. In the current study, the high-yielding MK <i>M. pilosus</i> MS-1 was used as the research object, and it was found that the enoyl reductase domain of MokA may be non-functional due to the lack of amino acids at active sites, a function that may be compensated for by MokE in the MK synthesis pathway. Then, the <i>mokE</i>-deleted (Δ<i>mokE</i>), -complemented (Δ<i>mokE::mokE</i>), and -overexpressed (<i>PgpdA-mokE</i>) strains were constructed, and the results showed that Δ<i>mokE</i> did not produce MK, and Δ<i>mokE::mokE</i> restored MK synthesis, while the ability of <i>PgpdA-mokE</i> to produce MK was increased by 32.1% compared with the original strain MS-1. These results suggest that the MokA synthesized by <i>Monascus</i> spp. must be assisted by MokE to produce MK, just as lovastatin produced by <i>A. terreus</i>, which provides clues for further genetic engineering to improve the yield of MK in <i>Monascus</i> spp.