Enzymatic synthesis of 1,3,6,8-tetrahydroxynaphthalene solely from malonylcoenzyme A by a fungal iterative type I polyketide synthase PKS1

The Colletotrichum lagenarium PKS1 gene encoding iterative type I polyketid e synthase of 1,3,6,8-tetrahydroxynaphthalene (T4HN) was overexpressed in A spergillus oryzae. SDS-PAGE analysis of the cell-free extract prepared from the transformant showed an intense band of 230000 which corresponded to th e molecular weight of the deduced PKS 1 protein. By using this cell-free ex tract, in vitro synthesis of T4HN was successfully confirmed as the first e xample of the fungal multi-aromatic ring polyketide synthase activity ever detected. To identify the starter unit fur T4HN synthesis, C-14-labeled ace tyl CoA and/or C-14-labeled malonyl CoA were used as substrates for T4HN sy nthase reaction. Observed was the incorporation of C-14 label into T4HN sol ely from malonyl CoA even in the absence of acetyl CoA and not from acetyl CoA. This in vitro result unambiguously identified that malonyl CoA serves as the starter as well as extender units in the formation of T4HN by fungal polyketide synthase PKS1.