Lavastatin biosynthesis in Aspergillus terreus: characterization of blocked mutants, enzyme activities and a multifunctional polyketide synthase gene

Background: Lovastatin, an HMG-CoA reductase inhibitor produced by the fung us Aspergillus terreus, is composed of two polyketide chains. One is a nona ketide that undergoes cyclization to a hexahydronaphthalene ring system and the other is a simple diketide, 2-methylbutyrate. Fungal polyketide syntha se (PKS) systems are of great interest and their genetic manipulation shoul d lead to novel compounds. Results: An A. terreus mutant (BX102) was isolated that could not synthesiz e the nonaketide portion of lovastatin and was missing a similar to 250 kDa polypeptide normally present under conditions of lovastatin production. Ot her mutants produced lovastatin intermediates without the methylbutyryl sid echain and were missing a polypeptide of similar to 220 kDa, The PKS inhibi tor cerulenin reacted covalently with both polypeptides, Antiserum raised a gainst the similar to 250 kDa polypeptide was used to isolate the correspon ding gene, which complemented the BX102 mutation. The gene encodes a polype ptide of 269 kDa containing catalytic domains typical of vertebrate fatty a cid and fungal PKSs, plus two additional domains not previously seen in PKS s: a centrally located methyltransferase domain and a peptide synthetase el ongation domain at the carboxyl terminus. Conclusions: The results show that the nonaketide and diketide portions of lovastatin are synthesized by separate large multifunctional PKSs, Elucidat ion of the primary structure of the PKS that forms the lovastatin nonaketid e, as well as characterization of blocked mutants, provides new details of lovastatin biosynthesis.