Chemistry: molecular biology and microbiology – Micro-organism – tissue cell culture or enzyme using process... – Recombinant dna technique included in method of making a...
Reexamination Certificate
1998-01-26
2001-11-27
Smith, Lynette R. F. (Department: 1649)
Chemistry: molecular biology and microbiology
Micro-organism, tissue cell culture or enzyme using process...
Recombinant dna technique included in method of making a...
C800S295000, C800S298000, C435S320100, C435S419000, C435S468000, C536S023700, C536S024100, C536S023200, C536S023740
Reexamination Certificate
active
06323001
ABSTRACT:
FIELD OF INVENTION
This invention relates to the genetic engineering of the trehalose synthetic pathway of yeasts, especially baker's and distiller's yeasts, and to the transfer of this pathway by genetic engineering to other organisms. It relates to the production of trehalose and ethanol and to the improvement of the stress resistance of organisms, especially yeasts and crop plants.
BACKGROUND OF THE INVENTION
It is well known that sugars and other polyhydric compounds stabilize isolated proteins and phospholipid membranes during dehydration, probably by replacing the water molecules that are hydrogen-bonded to these macromolecules [reviewed by Crowe, J. H. et al. (1987) Biochemical Journal 242, 1-10]. Trehalose (&agr;-glucopyranosyl-&agr;-D-glucopyranose) is a dimer of two glucose molecules linked through their reducing groups. Because it has no reducing groups, it does not take part in the Maillard reactions that cause many sugars to damage proteins, and it is one of the most effective known protectants of proteins and biological membranes in vitro.
In nature, trehalose is found at high concentrations in yeasts and other fungi, some bacteria, insects, and some litoral animals, such as the brine shrimp. It is notable that all these organisms are frequently exposed to osmotic and dehydration stress. Accumulation of trehalose in higher plants is rare, but high levels occur in the so-called resurrection plants, such as the pteridophyte,
Selaginella lepidophylla,
which can survive extended drought [Quillet, M. and Soulet, M. (1964) Comptes Rendus de l'Academie des Sciences, Paris 259, pp. 635-637; reviewed by Avigad, G. (1982) in Encyclopedia of Plant Research (New Series) 13A, pp. 217-347].
A decreased availability of intracellular water to proteins and membranes is a common feature not only of dehydration and osmotic stress, but also of freezing, in which ice formation withdraws water from inside the cells, and heat stress, which weakens the hydrogen bonds between water and biological macromolecules. In recent years several publications have shown a close connection between the trehalose content of yeast cells, especially of the species
Saccharomyces cerevisiae,
and their resistance to dehydration and osmotic, freezing and heat stresses. This work has lead to the concept [summarized by Wiemkem, A. (1990) Antonie van Leeuwenhoek 58, 209-217] that, whereas the main storage or reserve carbohydrate in yeast is glycogen, the prime physiological function of trehalose is as a protectant against these and other stresses, including starvation and even poisoning by copper, ethanol and hydrogen peroxide, which all stimulate trehalose accumulation [Attfield, P. V. (1987) Federation of European Biochemical Societies Letters 225, 259-263].
Thus, during growth of
Saccharomyces cerevisiae
on glucose, glycogen begins to accumulate about one generation before the glucose is exhausted, and begins to be steadily consumed as soon as all external carbon supplies are exhausted. In contrast, accumulation of trehalose (partly at the expense of glycogen) only begins after all the glucose has been consumed, and the trehalose level is then maintained until nearly all the glycogen has been consumed [Lillie, S. A. & Pringle, J. R. (1980) Journal of Bacteriology 143, 1384-1394]. The eventual consumption of trehalose is accompanied by a rapid decrease in the number of viable cells.
When trehalose levels in
S. cerevisiae
have been manipulated by varying the growth conditions or administering heat shocks, high positive correlations have been found between the trehalose content of the cells and their resistance to dehydration [Gadd, G. et al. (1987) Federation of European Microbiological Societies Microbiological Letters 48, 249-254], heat stress [Hottiger, T. et al., (1987) Federation of European Biochemical Societies Letters 220, 113-115] and freezing [Gélinas, P. et al. Applied and Environmental Microbiology 55, 2453-2459]. Also, strains of
S. cerevisiae
and other yeasts selected for resistance to osmotic stress [D'Amore, T. et al. (1991) Journal of Industrial Microbiology 7, 191-196] or high performance in frozen dough fermentation [Oda, Y. (1986) Applied and Environmental Microbiology 52, 941-943] were found to have unusually high trehalose contents. Furthermore, a mutation in the cyclic AMP signaling system of
S. cerevisiae
that causes constitutive high trehalose levels also causes constitutive thermotolerance, whereas another mutation in this system that prevents the usual rise in trehalose during heat shock also prevents the acquisition of thermotolerance [Hottiger, T. et al., (1989) Federation of European Biochemical Societies Letters 255, 431-434]. Thus, there is much evidence pointing to a connection between trehalose content and stress resistance in yeasts, especially
S. cerevisiae.
Similar findings have been made for several other fungi [e.g., Neves, M. J., Jorge, J. A., Francois, J. M. & Terenzi, H. F. (1991) Federation of European Biochemical Societies Letters 283, 19-22]. However, a causative relationship has not yet been demonstrated. Further, nearly all conditions that cause increases in the trehalose content of yeast also cause increases in the levels of the so-called heat shock proteins. The 1989 publication of Hottiger and colleagues, cited above, claims that canavanine does not cause an increase in either trehalose levels or thermotolerance, whereas this compound is reported to induce heat shock proteins.
Whether or not there is a causal relation between trehalose content and stress resistance, it has become general practice in the manufacture of baker's yeast to maximise the trehalose content of the yeast. Various maturation processes have been developed to achieve this aim, and they are of crucial importance in the manufacture of active dried yeast. The details of these processes are often secret, but they are generally empirical regimes in which carbon and nitrogen feeds, aeration and temperature are carefully controlled and selected strains of yeast are used. They demand time and energy inputs during which little increase in cell number occurs. A more rational and controlled process would be of economic benefit.
According to Cabib, E. & Leloir, L. F. [(1957) Journal of Biological Chemistry 231, 259-275], trehalose is synthesized in yeast from uridine diphosphoglucose (UDPG) and glucose-6-phosphate (G6P) by the sequential action of two enzyme activities, trehalose-6-phosphate synthase (Tre6P synthase) and trehalose-6-phosphate phosphatase (Tre6Pase). Londesborough, J. & Vuorio, O. [(1991) Journal of Microbiology 137, 323-330, expressly incorporated herein by reference] have purified from baker's yeast a proteolytically modified protein complex that exhibited both these activities and appeared to contain a short polypeptide chain (57 kDa) and two truncated versions (86 kDa and 93 kDa) of a long polypeptide chain. The intact long chain was estimated to have a mass of at least 115 kDa. It was not disclosed which enzyme activity or activities was associated with which polypeptide, nor indeed whether both polypeptides were essential for either or both enzymatic activities. Anti-sera against both polypeptides were reported, but no amino acid sequences were disclosed.
An earlier patent application [EP 451 896; see claim
1
] has claimed for a transformed yeast “comprising . . . one gene encoding . . . trehalose-6-phosphate synthase”. However, no information about either the gene or the protein it encodes was provided.
Several authors have reported increases in Tre6P synthase activity in conditions that lead to accumulation of trehalose by
S. cerevisiae,
and
Schizosaccharomyces pombe
both during the approach to stationary phase [Winkler, K., et al. (1991) Federation of European Biochemical Societies Letters 291, 269-272; Francois, J., et al. (1991) Yeast 7, 575-587] and after temperature
Holmstrom Kjell-Ove
Londesborough John
Mandal Abul
Palva Tapio
Tunnela Outi
BTG International Ltd.
Haas Thomas
Kubovcik & Kubovcik
Smith Lynette R. F.
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