Nucleic acid molecules encoding alternansucrase

Details Nucleic acid molecules encoding alternansucrase Nucleic acid molecules encoding alternansucrase

2000-02-08

2003-05-27

Fox, David T. (Department: 1638)

Multicellular living organisms and unmodified parts thereof and

Method of introducing a polynucleotide molecule into or...

The polynucleotide alters carbohydrate production in the plant

C800S278000, C800S288000, C800S305000, C800S306000, C800S312000, C800S314000, C800S317200, C800S320000, C800S320100, C800S320200, C800S320300, C800S322000, C435S069100, C435S070100, C435S071100, C435S101000, C435S193000, C435S252300, C435S252330, C435S320100, C435S419000, C435S468000, C435S471000, C435S476000, C536S023200, C536S023700

Reexamination Certificate

active

06570065

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to nucleic acid molecules encoding an alternansucrase. Moreover, this invention relates to vectors, host cells and plant cells transformed with the herein-described nucleic acid molecules, and plants containing said cells. Moreover, methods for preparing transgenic plants which due to the insertion of DNA molecules encoding an alternansucrase, synthesize the carbohydrate alternan, are described. Furthermore, methods for preparing alternan are described.
Prior art documents, the disclosure content of which is included into the present application by reference thereto, are cited hereinafter.
Alternan is a polysaccharide composed of glucose units. The glucose units are linked to each other via &agr;-1,3- and &agr;-1,6-glycosidic bonds, and said two types of bonds predominantly appear alternatingly. However, alternan is not a linear polysaccharide, but may contain branches (Seymour et al., Carbohydrate Research 74, (1979), 41-62). Because of its physico-chemical properties, the possibilities of application of alternan both in the pharmaceutical industry, for instance as a carrier of pharmaceutically active ingredients and as an additive in the textile, cosmetics and food industry have been discussed (Lopez-Munguia et al., Enzyme Microb. Technol. 15, (1993), 77-85; Leathers et al., Journal of Industrial Microbiology & Biotechnology 18, (1997), 278-283). Moreover, it can be used as a substitute for gum arabic (Coté, Carbohydrate Polymers 19, (1992), 249-252).
Industry has a high interest in biotechnological methods for preparing oligosaccharides and polysaccharides, and in particular alternan which is hardly or not at all accessible to classical organic synthesis. Compared to the classical approach of organic synthesis chemistry, biotechnological processes offer advantages. For instance, enzymatically catalyzed reactions as a rule show much higher specificities (regio specificity, stereo specificity) and higher reaction speeds, proceed under milder reaction conditions and lead to higher yields. These factors are of outstanding importance in the preparation of new oligosaccharides and polysaccharides.
Alternan is prepared enzymatically with the use of enzymes possessing the biological activity of alternansucrases. Alternansucrases belong to the group of glucosyltransferases, which, starting from saccharose, are able to catalyze the formation of alternan and fructose. So far, alternansucrases have only been found in the bacterium
Streptococcus mutans
(Mukasa et al. (J. Gen. Microbiol. 135 (1989), 2055-2063); Tsumori et al. (J. Gen. Microbiol. 131 (1985), 3347-3353)) and in specific strains of the gram positive bacterium
Leuconostoc mesenteroides
where they are, as a rule, present together with other polysaccharide-forming enzymes, such as for instance dextran-forming dextransucrases, or together with polysaccharide-degrading enzymes, such as alternanases. Hence, the naturally occurring strains also produce dextran in addition to alternan.
So far, alternan has been prepared in a cell-free system using partially purified proteins or by fermentation using alternansucrase-producing strains of
Leuconostoc mesenteroides.
Various purification methods for the purification of alternansucrases have been described (Lopez-Munguia et al., Enzyme Microb. Technol. 15 (1993), 77-85; Lopez-Munguia et al., Annals New York Academy of Sciences 613 (1990), 717-722; Coté and Robyt, Carbohydrate Research 101 (1982), 57-74). These methods are complex and relatively costly, and, as a rule, lead to low protein yields (Leathers et al., Journal of Industrial Microbiology & Biotechnology 18 (1997), 278-283). None of these methods allows highly pure alternansucrase protein to be produced, and therefore sequencing of the protein and the isolation of the corresponding DNA sequences have not been successful so far. If the alternansucrase protein purified according to these methods is used for in vitro preparation of alternan, then the dextransucrase protein residues contained in the alternansucrase preparation produce dextran impurities in the alternan produced. The separation of alternan and dextran is relatively time-consuming and costly (Leathers et al., Journal of Industrial Microbiology & Biotechnology 18 (1997), 278-283). Another disadvantage of the dextransucrase protein impurities contained in the enzyme preparation of alternansucrase protein is the fact that a part of the saccharose substrate is converted into dextran and not into alternan, which results in a reduction of the alternan yield.
The fermentative preparation by means of Leuconostoc also leads to the formation of product mixtures of alternan and dextran. In order to increase the amount of alternansucrase from Leuconostoc strains, mutants have been isolated, such as the mutant NRRL B-21138, which secrete the alternansucrase and lead to a higher proportion of the amount of alternansucrase formed relative to dextransucrase. However, if such mutants are fermented with sucrose, the alternan obtained continues to show dextran impurities (Leathers et al., Journal of Industrial Microbiology & Biotechnology 18 (1997), 278-283).
As can be seen from the prior art discussed above, it has not been possible to provide highly purified alternansucrase protein so far.
Hence, the present invention addresses the problem of providing means and methods allowing alternan to be prepared in a time-saving and inexpensive manner.
This problem is solved by the provision of the embodiments characterized in the patent claims.
SUMMARY OF THE INVENTION
Consequently, the present invention relates to a nucleic acid molecule encoding a protein possessing the biological activity of an alternansucrase selected from the group consisting of
(a) nucleic acid molecules encoding at least the mature form of a protein which comprises the amino acid sequence indicated in Seq. ID No. 2 or the amino acid sequence encoded by the cDNA contained in plasmid DSM 12666;
(b) nucleic acid molecules comprising the nucleotide sequence indicated in Seq. ID No. 1 or the nucleotide sequence of the cDNA contained in plasmid DSM 12666 or a corresponding ribonucleotide sequence;
(c) nucleic acid molecules encoding a protein, the amino acid sequence of which has a homology of at least 40% to the amino acid sequence indicated in Seq. ID No. 2;
(d) nucleic acid molecules, one strand of which hybridizes with the nucleic acid molecules as defined in (a) or (b);
(e) nucleic acid molecules comprising a nucleotide sequence encoding a biologically active fragment of the protein which is encoded by any one of the nucleic acid molecules as defined in (a), (b), (c) or (d); and
(f) nucleic acid molecules, the nucleotide sequence of which deviates because of the degeneration of the genetic code from the sequence of the nucleic acid molecules as defined in (a), (b), (c), (d) or (e).
Consequently, the present invention relates to nucleic acid molecules encoding proteins possessing the biological activity of an alternansucrase, said molecules preferably encoding proteins comprising the amino acid sequence indicated in Seq. ID No.2.
An enzyme possessing the enzymatic or biological activity of an alternansucrase (E.C. 2.4.1.140) is understood to mean an enzyme which is able to catalyze the conversion of saccharose into alternan and fructose. This conversion may occur both in the presence and absence of external acceptors (for instance maltose, isomaltose, isomaltotriose etc.). In the absence of external acceptors, alternansucrases starting from saccharose catalyze the release of fructose and high molecular alternan, a polysaccharide composed of glucose units, the backbone of which consists of glucose units predominantly connected to each other alternatingly by &agr;-1,3- and &agr;-1,6-glycosidic bonds. Concerning the percentage of &agr;-1,3- and &agr;-1,6-linked glucose units the literature displays different values. According to Mukasa et al. (J. Gen. Microbiol. 135 (1989), 2055-2063), alternan consists of 76 mol % &agr;-1,3-linked glucose and 24 mol % &agr;-1,6-link

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