Recombinant oleandolide polyketide synthase

Details Recombinant oleandolide polyketide synthase Recombinant oleandolide polyketide synthase

1999-10-28

2001-06-26

Achutamurthy, Ponnathapu (Department: 1652)

Chemistry: molecular biology and microbiology

Micro-organism, tissue cell culture or enzyme using process...

Preparing compound containing saccharide radical

C435S320100, C435S252350, C435S254200, C435S325000, C435S419000, C536S023100, C536S023200

Reexamination Certificate

active

06251636

ABSTRACT:

FIELD OF THE INVENTION
The present invention provides recombinant methods and materials for producing polyketides by recombinant DNA technology. The invention relates to the fields of agriculture, animal husbandry, chemistry, medicinal chemistry, medicine, molecular biology, pharmacology, and veterinary technology.
BACKGROUND OF THE INVENTION
Polyketides represent a large family of diverse compounds synthesized from 2-carbon units through a series of condensations and subsequent modifications. Polyketides occur in many types of organisms, including fungi and mycelial bacteria, in particular, the actinomycetes. There are a wide variety of polyketide structures, and the class of polyketides encompasses numerous compounds with diverse activities. Erythromycin, FK-506, FK-520, narbomycin, oleandomycin, picromycin, rapamycin, spinocyn, and tylosin are examples of such compounds. Given the difficulty in producing polyketide compounds by traditional chemical methodology, and the typically low production of polyketides in wild-type cells, there has been considerable interest in finding improved or alternate means to produce polyketide compounds. See PCT publication Nos. WO 93/13663; WO 95/08548; WO 96/40968; 97/02358; and 98/27203; U.S. Pat. Nos. 4,874,748; 5,063,155; 5,098,837; 5,149,639; 5,672,491; and 5,712,146; Fu et al., 1994,
Biochemistry
33: 9321-9326; McDaniel et al., 1993,
Science
262: 1546-1550; and Rohr, 1995,
Angew. Chem. Int. Ed Engl.
34(8): 881-888, each of which is incorporated herein by reference.
Polyketides are synthesized in nature by polyketide synthase (PKS) enzymes. These enzymes, which are complexes of multiple large proteins, are similar to the synthases that catalyze condensation of 2-carbon units in the biosynthesis of fatty acids. Two major types of PKS enzymes are known; these differ in their composition and mode of synthesis. These two major types of PKS enzymes are commonly referred to as Type I or “modular” and Type II “iterative” PKS enzymes.
Modular PKSs are responsible for producing a large number of 12-, 14-, and 16-membered macrolide antibiotics including erythromycin, methymycin, narbomycin, oleandomycin, picromycin, and tylosin. Modular PKS enzymes for 14-membered polyketides are encoded by PKS genes that often consist of three or more open reading frames (ORFs). Each ORF of a modular PKS can comprise one, two, or more “modules” of ketosynthase activity, each module of which consists of at least two (if a loading module) and more typically three (for the simplest extender module) or more enzymatic activities or “domains.” These large multifunctional enzymes (>300,000 kDa) catalyze the biosynthesis of polyketide macrolactones through multistep pathways involving decarboxylative condensations between acyl thioesters followed by cycles of varying &bgr;-carbon processing activities (see O'Hagan, D.
The polyketide metabolites
; E. Horwood: New York, 1991, incorporated herein by reference).
During the past half decade, the study of modular PKS function and specificity has been greatly facilitated by the plasmid-based
Streptomyces coelicolor
expression system developed with the 6-deoxyerythronolide B (6-dEB) synthase (DEBS) genes (see Kao et al., 1994,
Science,
265: 509-512, McDaniel et al., 1993,
Science
262: 1546-1557, and U.S. Pat. Nos. 5,672,491 and 5,712,146, each of which is incorporated herein by reference). The advantages to this plasmid-based genetic system for DEBS are that it overcomes the tedious and limited techniques for manipulating the natural DEBS host organism,
Saccharopolyspora erythraea,
allows more facile construction of recombinant PKSs, and reduces the complexity of PKS analysis by providing a “clean” host background. This system also expedited construction of the first combinatorial modular polyketide library in Streptomyces (see PCT publication No. WO 98/49315, incorporated herein by reference).
The ability to control aspects of polyketide biosynthesis, such as monomer selection and degree of &bgr;-carbon processing, by genetic manipulation of PKSs has stimulated great interest in the combinatorial engineering of novel antibiotics (see Hutchinson, 1998,
Curr. Opin. Microbiol.
1: 319-329; Carreras and Santi, 1998,
Curr. Opin. Biotech.
9: 403-411; and U.S. Pat. Nos. 5,712,146 and 5,672,491, each of which is incorporated herein by reference). This interest has resulted in the cloning, analysis, and manipulation by recombinant DNA technology of genes that encode PKS enzymes. The resulting technology allows one to manipulate a known PKS gene cluster either to produce the polyketide synthesized by that PKS at higher levels than occur in nature or in hosts that otherwise do not produce the polyketide. The technology also allows one to produce molecules that are structurally related to, but distinct from, the polyketides produced from known PKS gene clusters.
Oleandomycin is an antibacterial polyketide (described in U.S. Pat. No. 2,757,123, incorporated herein by reference) produced by a modular PKS in
Streptomyces antibioticus
. Oleandomycin has the structure shown below, with the conventional numbering scheme and stereochemical representation.
As is the case for certain other macrolide antibiotics, the macrolide product of the PKS, 8,8a-deoxyoleandolide, also referred to herein simply as oleandolide (although oleandolide in other contexts refers to the epoxidated aglycone), is further modified by epoxidation (at C-8 and C-8a) and glycosylation (an oleandrose at C-3 and a desosamine at C-5) to yield oleandomycin.
The reference Swan et al., 1994, entitled “Characterisation of a
Streptomyces antibioticus
gene encoding a type I polyketide synthase which has an unusual coding sequence,”
Mol. Gen. Genet.
242: 358-362, incorporated herein by reference, describes the DNA sequence of the coding region of a gene designated ORFB hypothesized to encode modules 5 and 6 and a fragment of a gene designated ORFA hypothesized to contain the ACP domain of module 4 of the oleandolide PKS. The reference Quiros et al., 1998, entitled “Two glycosyltransferases and a glycosidase are involved in oleandomycin modification during its biosynthesis by
Streptomyces antibioticus,” Mol. Microbiol.
28(6): 1177-1185, incorporated herein by reference, describes genes and gene products involved in oleandomycin modification during its biosynthesis. In particular, the reference describes a glycosyltransferase involved in rendering oleandomycin non-toxic to the producer cell and a glycosidase that reactivates oleandomycin after the glycosylated form is excreted from the cell. See also Olano et al., August 1998, “Analysis of a
Streptomyces antibioticus
chromosomal region involved in oleandomycin biosynthesis, which encodes two glycosyltransferases responsible for glycosylation of the macrolactone ring,
Mol. Gen. Genet.
259(3): 299-308, and PCT patent publication No. 99/05283, incorporated herein by reference. While a number of semi-synthetic oleandomycin derivatives have been described, see U.S. Pat. Nos. 4,085,119; 4,090,017; 4,125,705; 4,133,950; 4,140,848; 4,166,901; 4,336,368; and 5,268,462, incorporated herein by reference, the number and diversity of such derivatives have been limited due to the inability to manipulate the PKS genes.
Genetic systems that allow rapid engineering of the oleandolide PKS would be valuable for creating novel compounds for pharmaceutical, agricultural, and veterinary applications. The production of such compounds could be accomplished if the heterologous expression of the oleandolide PKS in
Streptomyces coelicolor
and
S. lividans
and other host cells were possible. The present invention meets these and other needs.
SUMMARY OF THE INVENTION
The present invention provides recombinant methods and materials for expressing PKS enzymes derived in whole and in part from the oleandolide PKS in recombinant host cells. The invention also provides the polyketides produced by such PKS enzymes. The invention provides in recombinant form all of the genes for the proteins that constitute the complete PKS that ul

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