Chemistry: molecular biology and microbiology – Micro-organism – tissue cell culture or enzyme using process... – Preparing heterocyclic carbon compound having only o – n – s,...
Reexamination Certificate
2000-08-09
2003-12-30
Nashed, Nashaat T. (Department: 1652)
Chemistry: molecular biology and microbiology
Micro-organism, tissue cell culture or enzyme using process...
Preparing heterocyclic carbon compound having only o, n, s,...
C435S119000, C435S118000, C435S117000
Reexamination Certificate
active
06670157
ABSTRACT:
The present invention relates to novel polypeptides involved in the biosynthesis of streptogramins, and also comprises the isolation and identification of genes for the biosynthesis of the A and B components of streptogramins, the expression of these genes with the object of increasing the levels of production and their use for the construction of blocked mutants capable of leading to the synthesis of novel antibiotics or to derived forms of streptogramins.
Streptogramins form a homogeneous group of antibiotics, consisting of a combination of two types of molecules which are chemically different; on the one hand polyunsaturated macrolactones (A-group components, two examples of structures of which are presented in FIG.
1
), and on the other hand depsipeptides (B-group components, three examples of the structure of which are presented in FIG.
2
). This group comprises many antibiotics (see Table 1 and FIG.
3
), which are known by different names in accordance with their origin, including pristinamycins, mikamycins and virginiamycins (for a review, see Cocito 1979, 1983).
The A and B components have a synergistic antibacterial activity which can reach 100 times that of the separate components and which, in contrast to that of each component, is bactericidal (Cocito 1979). This activity is more especially effective against Gram-positive bacteria such as staphylococci and streptococci (Cocito 1979, Videau 1982). The A and B components inhibit protein synthesis by binding to the 50S subunit of the ribosome (Cocito 1979; for a review, see Di Giambattista et al. 1989).
Streptogramins are chiefly produced by actinomycetes, including many streptomycetes, presented in Table 1. In addition, streptogramins are also synthesized by eukaryotes such as Micromonospora which synthesizes vernamycins. Actinomycetes constitute a very important group of microorganisms on account of the large amount of secondary metabolites they produce, including many.antibiotics (beta-lactams, tetracyclines, macrolides, aminoglycosides, polyacetates and the like), herbicides, anticancer agents, antifungal agents, immunomodulators and enzyme inhibitors. Many biosynthesis pathways relating to antibiotics belonging to miscellaneous classes as well as other secondary metabolites such as pigments (for a review, Chater 1990) have already been studied at the present time in actinomycetes. An important aspect of this group of bacteria is that the genes involved in the same biosynthesis pathway, structural genes and also resistance gene(s) and regulatory gene(s), are grouped together physically on the chromosome, constituting clusters which can reach more than 100 kb (Hopwood et al. 1986a, Hopwood et al. 1986b, Hallam et al. 1988, Anzai et al. 1987, Ohnuki et al. 1985). To date, no example has been found to contradict this observation. Such a structural organization is of great interest in the development of strategies for cloning biosynthesis genes. In effect, it is possible, starting from a single gene previously cloned by various techniques, a biosynthesis, resistance or regulatory gene, to walk along the chromosome and thus to isolate the set of genes of the biosynthesis cluster.
Our knowledge of the biosynthesis pathways of each of the components of streptogramins is still very incomplete, but the origin of the different parts of each molecule has been identified by radioactive labelling (Kingston et al. 1983). Thus, the A-type components are made up of two regions originating from the condensation of acetates and several amino acids such as serine and glycine, for example. As regards the B-type components, studies have shown that all the amino acids present in the peptide chain are derived from natural amino acids (Hook and Vining 1973). However, no polypeptide involved in these pathways has, to date, been purified in sufficient amounts to permit its molecular characterization, and no biosynthesis gene has been described. In the process of biosynthesis of the B-type components, two parts may be distinguished:
1) Synthesis of the precursors, or of their analogues, of the macrocycle: 3-hydroxypicolinic acid, L-2-aminobutyric acid, p-dimethylamino-L-phenylalanine, 4-oxo-L-pipecolic acid, L-phenylglycine.
2) Formation of the macrocycle from the precursors mentioned above, L-threonine and L-proline, or their analogues, with possible modification of these precursors or peptide N-methylation.
To date, only the probable metabolic origin of the precursors of the macrocycle of the B-type components has been determined by studies using labelled isotopes (Reed et al., 1986, Molinero et al., 1989, Reed et al., 1989).
The present invention results from the purification of polypeptides participating in the biosynthesis of streptogramins, as well as from the cloning of genes whose product participates in the biosynthesis of streptogramins. The term biosynthesis of streptogramins is understood to comprise the regulatory genes and the genes conferring resistance on the producing microorganisms. Thus, the present invention makes it possible to increase the levels of production of these metabolites by means of recombinant DNA techniques. Another benefit of the present invention lies in the possibility, by construction of mutants blocked in the different steps of this biosynthesis, of producing synthesis intermediates for each of the two components. These intermediates may serve as substrates for further modification for chemical, biochemical, enzymatic or microbiological means. Similarly, isolation of the biosynthesis genes makes it possible, by gene transfer between producing strains, to manufacture hybrid antibiotics having pharmacologically advantageous properties (Hopwood et al., 1985a, Hopwood et al., 1985b, Hutchinson et al. 1989). Another benefit of the present invention lies in the fact that it provides a better knowledge of the biosynthesis pathways of the metabolites classed as streptogramins. In effect, the invention enables bacterial or fungal strains to be constructed in which one or more proteins participating in the biosynthesis of streptogramins is/are expressed under the control of suitable expression signals. Such strains may then be used to carry out bioconversions. These bioconversions may be carried out either using whole cells, or using acellular extracts of the said cells. These bioconversions may enable a streptogramin to be converted to a derived form with an enzyme of a biosynthesis pathway. For example, pristinamycin IIB may be converted in this manner to pristinamycin IIA. The same reasoning may be applied to any biosynthesis intermediate.
A first subject of the invention hence relates to a nucleotide sequence coding for a polypeptide involved in the biosynthesis of streptogramins.
More especially, several genes whose product participates in the biosynthesis of streptogramins have been isolated from
Streptomyces pristinaespiralis.
Since the streptogramins produced by this strain are more commonly designated by the term pristinamycins (see Table 1), in what follows, reference will be made in some cases to genes for the biosynthesis of pristinamycins. However, it is clear that the results obtained apply to all the streptogramins. Pristinamycins I and II correspond, respectively, to the B and A components of streptogramins. Molecules of the pristinamycin II family and of the pristinamycin I family hence designate in what follows the A and B components of streptogramins, respectively.
The present invention describes in particular the isolation and characterization of the snaA, snaB, snaC, snaD, papA, papM, samS, snbA, snbC, snbD, snbE and snbR genes. These genes were isolated from a library of genomic DNA of
S.pristinaespiralis.
This library was obtained by partial digestion of genomic DNA
S.pristinaespiralis
with the restriction enzyme Sau3A. Large DNA fragments, from 40 to 50 kb on average, were cloned into cosmid pEC79 (Hohn, B., and Collins, J. F., 1980). After in vitro encapsidation,
E.coli
strains HB101 (Boyer et Roulland-Dussoix, 1969) and DH1 (Low, 1968) were transfected. The DNA library of
S
Blanc Veronique
Blanche Francis
Crouzet Joel
De Crecy-Lagard Valerie
Debussche Laurent
Aventis Pharma S.A.
Finnegan Henderson Farabow Garrett & Dunner LLP
Nashed Nashaat T.
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