Marine organisms have attracted attention as an important source for development of new medicines. In particular, marine microorganisms have been known to produce secondary metabolites having various structures and activities. The marine microorganisms often produce natural bioactive substances different from the species found in land environments as the biochemical metabolisms in the body are adapted to marine environments (salinity, a pressure, a high-concentration halogen, etc.) which are completely different from the land environments (Fenical and Jensen 2006; Marris 2006).
New 17-membered carbocyclic tetraene natural substances, chejuenolides A, B and C, have been found from a culture extract of a marine microorganism Hahella chejuensis MB-1084 isolated from a marine sediment within the intertidal region in coastal waters of Geojedo Island (Choi, Sohn et al. 2008; Seo and Oh 2009). Only an antibiotic, lankacidin, isoliated from Streptomyces greseofuscus, S. violaceoniger, and S. rochei var. volubilis was previously reported as the antibiotic containing a 17-membered carbocyclic ring (Uramoto, Otake et al. 1969; Higashide, Fugono et al. 1971). Lankacidin is a very powerful antibacterial agent that is currently used to treat an infection of Serpulina (Treponema) hyodysenteriae that is a type of bacteria called a spirochete causing diseases in animals and also known to have an anticancer activity and an immunosuppressive effect (Oostu, Matsumoto et al. 1975; Hayashi, Suenaga et al. 1988). Lankacidin have various kinds of analogs (some analogs are also referred to as T-2636 or bundlins). In this case, lankacidin C and chejuenolide highly resemble each other in a structural aspect (Harada and Kishi 1974; Harada 1975; Nakahama, Harada et al. 1975). However, the lankacidin is different from the chejuenolide in that the lankacidin has a 6-membered-δ-lactone ring structure in a 17-membered macrocyclic ring and a 2-hydroxy-propanamide chain at a 3rd carbon atom (Harada and Kishi 1974; Harada 1975; Choi, Sohn et al. 2008). It was reported that δ-lactone rings are disrupted as the metabolites, lankacyclinol and lankacyclinol A (12-O-acetyl lankacyclinol), obtained after administration of lankacidin C into rats undergo a decarboxylation action, but a macrolide-based polyketide natural substance having a 17-membered carbocyclic tetraene residue without a 6-membered-δ-lactone ring (deficient in ester bonds) is only a chejuenolide (Harada, Tanayama et al. 1973; Choi, Sohn et al. 2008).
The polyketide-based natural substance is one of the secondary metabolites from the microorganisms which are of medicinal importance, and belong to the antibiotics (tetracycline, erythromycin A, rifamycin S, etc.), the anticancer drugs (daunorubicin, epothilone, etc.), the cholesterol lowering agents (lovastatin, etc.), the anthelminthics (Avermectin, etc.), the antimicrobial drugs (Amphotericin B, etc.), the pesticides (Spinosy A, etc.), and the immunosuppressive drugs (rapamycin, FK506, etc.) (Staunton and Weissman 2001; Shen 2003).
A polyketide is biosynthesized by several simple condensation reactions of carboxylic acid by a polyketide synthase (PKS), a pathway of which is similar to the biosynthesis pathway of fatty acid (Shen 2003; Muller 2004). Type I polyketide is biosynthesized by type I PKS that is a huge multifunctional enzyme, one protein of which shows various enzymatic activities. In this case, such a PKS complex is composed of several modules associated with consecutive condensation reactions (Gokhale, Tsuji et al. 1999; Muller 2004). Each of the modules is composed of acyl transferase (AT), acyl carrier protein (ACP) and β-ketoacyl synthase (KS) domains, which are directly associated with the condensation reaction of carboxylic acid, and ketone reductase (KR), dehydratase (DH) and enoyl reductase (ER) domains which are associated with the reduction of β-ketone groups produced as a result of the condensation reaction (Kennedy, Auclair et al. 1999). The type of carboxylic acid that is an extension unit used in each condensation reaction is widely determined according to the characteristics of the AT domains of each module, a level of reduction of β-ketone groups produced as a result of the condensation reaction varies according to the presence of the reduction domains (KR, DH, and ER) in each module, and the length of the polyketide chain is determined according to the total number of the modules (Donadio and Katz 1992; MacNeil, Occi et al. 1992; Aparicio, Molnar et al. 1996). That is, polyketides having various structures may be biosynthesized according to the combinations of the respective modules and domains. In this aspect, PKS has become an important study subject for combinatorial biosynthesis in addition to a non-ribosomal peptide synthetase (NRPS; a peptide synthetase that is not synthesized in the ribosomes) (Cortes, Wiesmann et al. 1995; Hutchinson and Fujii 1995; Oliynyk, Brown et al. 1996; Jacobsen, Hutchinson et al. 1997; Katz 1997; McDaniel, Thamchaipenet et al. 1999; Menzella, Reid et al. 2005).
The marine microorganism H. chejuensis biosynthesizes a polyketide chejuenolide having a peculiar 17-membered macrocyclic structure. When enzymes contributing to the biosynthesis pathway of chejuenolide, and genes encoding the enzymes are elucidated and then applied to development of novel materials as a mechanism for combinatorial biosynthesis, there is a high probability of addressing the new directionality to studies of polyketide-based antibiotics. As the prior-art technique of the present invention, Korean Registered Patent No. 10-0661175 (Dec. 22, 2006) discloses an algicidal preparation including prodigiosin and a prodigiosin biosynthetic gene cluster, and Japanese Unexamined Patent Laid-open Publication No. JP P2006-296419A (Nov. 2, 2006) discloses a method for producing an antibiotic-producing microorganism by gene disruption and the resultant antibiotic-producing microorganism and a method for producing an antibiotic metabolic intermediate (Wnashi Y. and Arakawa K. (2006).). Also, U.S. Pat. No. 4,914,206 (Apr. 3, 1900) discloses lankacidin derivatives and a production method thereof (Minamida. I. and Hashimoto N. (1993) Lankacidin derivatives and production thereof; JP62240687 (Oct. 21, 1987), U.S. Pat. No. 4,914,206 (Apr. 3, 1990), CN1014050 (Jun. 20, 1993), and EP00226896 (Sep. 15, 1993)). However, the isolated gene cluster required to biosynthesize a chejuenolide, and the functions of enzymes encoded by the gene cluster remains to be elucidated.