In vivo and in vitro analysis of the hedamycin polyketide synthase.
Hedamycin is an antitumor polyketide antibiotic with unusual biosynthetic features. Earlier sequence analysis of the hedamycin biosynthetic gene cluster implied a role for type I and type II polyketide synthases (PKSs). We demonstrate that the hedamycin minimal PKS can synthesize a dodecaketide backbone. The ketosynthase (KS) subunit of this PKS has specificity for both type I and type II acyl carrier proteins (ACPs) with which it collaborates during chain initiation and chain elongation, respectively. The KS receives a C(6) primer unit from the terminal ACP domain of HedU (a type I PKS protein) directly and subsequently interacts with the ACP domain of HedE (a type II PKS protein) during the process of chain elongation. HedE is a bifunctional protein with both ACP and aromatase activity. Its aromatase domain can modulate the chain length specificity of the minimal PKS. Chain length can also be influenced by HedA, the C-9 ketoreductase. While co-expression of the hedamycin minimal PKS and a chain-initiation module from the R1128 PKS yields an isobutyryl-primed decaketide, the orthologous PKS subunits from the hedamycin gene cluster itself are unable to prime the minimal PKS with a nonacetyl starter unit. Our findings provide new insights into the mechanism of chain initiation and elongation by type II PKSs.
Das
Abhirup
A
Department of Chemistry, Stanford University, CA 94305-5025, USA.
Khosla
Chaitan
C
D000213:Acyl Carrier Protein / Q000378:metabolism; D000880:Anthraquinones / Q000737:chemistry*; D000903:Antibiotics, Antineoplastic / Q000096:biosynthesis* / Q000737:chemistry; D018942:Macrolides / Q000737:chemistry; D005810:Multigene Family; D048630:Polyketide Synthases / Q000235:genetics / Q000378:metabolism*; D013302:Streptomyces / Q000201:enzymology / Q000235:genetics
D000213:Acyl Carrier Protein; D000880:Anthraquinones; D000903:Antibiotics, Antineoplastic; D018942:Macrolides; C001328:hedamycin; D048630:Polyketide Synthases