Structural Organization of A Multifunctional Polyketide Synthase Involved in the Biosynthesis of the Macrolide Immunosuppressant FK506

Abstract

The immunosuppressant FK506 is a 23-membered macrocyclic polyketide produced by several Streptomyces species. Sequencing of a 19.5-kb contiguous segment of DNA from the FK506 gene cluster of Streptomyces sp. MA6548 revealed the presence of a single 19.3-kb open reading frame designatedfkbA. fkbA encodes a component of the FK506 polyketide synthase, a complex enzyme system which catalyzes synthesis of the polyketide portion of FK506. The predicted product of genefkbA is a 630660-Da protein (6420 amino acids) that contains 1 9 independent domains with a high degree of amino acid sequence similarity to the catalytic activities of known fatty acid synthases. The identified domains are arranged into four repeated modules with a linear organization precisely as that of animal fatty acid synthase and type I polyketide synthase. Each module participates in one round of chain extension and subsequent processing and thus FkbA polypeptide catalyzes four of the ten condensation steps required for synthesis of the FK506 macrolactone ring. Disruption of jkbA results in the generation of an FK506 non-producing mutant demonstrating direct involvement of fkbA in the biosynthesis of FK506.

Biosynthesis of the immunosuppressants FK506, FK520, and rapamycin involves a previously undescribed family of enzymes acting on chorismate

“…Initial comparison of the biosynthetic gene clusters for rapamycin (15)(16)(17), FK506 (26,27), and FK520 (28) did not reveal obvious candidate genes encoding the enzymes of such a pathway. However, detailed genetic analysis has since revealed an essential role for rapK in the production of DHCHC during rapamycin biosynthesis (29).…”

Involvement of the fadD33 gene in the growth of Mycobacterium tuberculosis in the liver of BALB/c mice

“…In this context, we also have to consider that FadD33 is similar to the putative polyketide biosynthesis protein PKSJ of Bacillus subtilis (Albertini et al, 1995), as it shows a 27n1 % identity in an overlap of 468 aa (http :\\ genolist.pasteur.fr\TubercuList\). As microbial polyketide metabolites have shown potent biological activities in different models, acting as virulence factors, antibiotics, immunosuppressants and toxins (George et al, 1999 ;Kolattukudy et al, 1997 ;Motamedi et al, 1997), it is tempting to consider that mycobacterial FadD33 might be involved in the synthesis of polyketides that play a role in M. tuberculosis infection in the liver. The involvement of certain polyketide metabolites in M. tuberculosis infection has been reported by Graham & Clark-Curtiss (1999), who showed that pks2, one of the 18 polyketide synthase genes of M. tuberculosis H37Rv, is expressed in infected human macrophages but not in bacteria growing in culture broth, and by De Voss et al (2000), who demonstrated that the mycobactin siderophores produced by polyketide synthase enzymes are essential for M. tuberculosis growth in macrophages.…”

Roles of fkbN in Positive Regulation and tcs7 in Negative Regulation of FK506 Biosynthesis in Streptomyces sp. Strain KCTC 11604BP

“…strain ATCC 55098 (MA6858) (26), Streptomyces sp. strain ATCC 53770 (MA6548) (25), and S. tsukubaensis NRRL 18488 (8). Recently, the sequences of the entire FK506 biosynthetic gene clusters from Streptomyces sp.…”