Directed evolution of operon of trehalose-6-phosphate synthase/phosphatase from Escherichia coli

Salt stress and hydroxyectoine enhance phosphate solubilisation and plant colonisation capacity of Kosakonia radicincitans

Gram-negative bacterial endophytes have attracted research interest caused by their advantageous over epiphytic bacteria in plant nutrition and protection. However, research on these typically Gram-negative endophytes has deficiencies concerning the role of cultivation and pre-formulation strategies on further plant colonisation capabilities. Besides, the influence of cultivation conditions and osmotic stress within bacterial endophytes on their phosphate solubilising ability has not yet been addressed. By pre-conditioning cells with an osmoadaptation and a hydroxyectoine accumulation approach, this research aimed at enhancing the capability of the plant growth promoting bacterium Kosakonia radicincitans strain DSM 16656T to both solubilise phosphate and colonise plant seedlings. The results showed that halotolerant bacterial phenotypes increased the root-colonising capability by approximately 3-fold and presented growth-promoting effects in radish plants. Interestingly, findings also demonstrated that salt stress in the culture media along with the accumulation of hydroxyectoine led to an increase in the in vitro phosphate-solubilising ability by affecting the production of acid phosphatases, from 1.24 to 3.34 U mg-1 for non-salt stressed cells and hydroxyectoine-added cells respectively. Thus, this approach provides a useful knowledge upon which the salt stress and compatible solutes in bacteria endophytes can confer phenotypic adaptations to support the eco-physiological performance concerning phosphate-solubilising abilities and endosphere establishment.

Expression Profiles of the Trehalose-6-Phosphate Synthase Gene Associated With Thermal Stress in Ostrinia furnacalis (Lepidoptera: Crambidae)

Trehalose is the major blood sugar in insects. Physiological significance of this compound has been extensively reported. Trehalose-6-phosphate synthase (TPS) is an important enzyme in the trehalose biosynthesis pathway. Full-length cDNAs of TPS (Of tps) and its alternative splicing isoform (Of tps_isoformI) were cloned from the Asian corn borer (ACB), Ostrinia furnacalis (Guenée; Lepidoptera: Crambidae) larvae. The Of tps and Of tps_isoformI transcripts were 2913 and 1689 bp long, contained 2529 and 1293 bp open reading frames encoding proteins of 842 and 430 amino acids with a molecular mass of 94.4 and 48.6 kDa, respectively. Transcriptional profiling and response to thermal stress of Of tps gene were determined by quantitative real-time PCR showing that the Of tps was predominantly expressed in the larval fat body, significantly enhanced during molting and transformation; and thermal stress also induced Of tps expression. Gene structure analysis is indicating that one TPS domain and one trehalose-6-phosphate phosphatase (TPP) domain were located at the N- and C-termini of Of        TPS, respectively, while only the TPS domain was detected in OfTPS_isoformI. Three-dimensional modeling and heterologous expression were developed to predict the putative functions of OfTPS and Of   TPS_isoformI. We infer that the expression of Of tps gene is thermally induced and might be crucial for larvae survival.

Characterization of a trehalose-6-phosphate synthase gene from Spodoptera exigua and its function identification through RNA interference

Trehalose is an important disaccharide and a key regulation factor for the development of many organisms, including plants, bacteria, fungi and insects. In order to study the trehalose synthesis pathway, a cDNA for a trehalose-6-phosphate synthase from Spodoptera exigua (SeTPS) was cloned which contained an open reading frame of 2481 nucleotides encoding a protein of 826 amino acids with a predicted molecular weight of 92.65kDa. The SeTPS genome has 12 exons and 11 introns. Northern blot and RT-PCR analyses showed that SeTPS mRNA was expressed in the fat body and in the ovary. Competitive RT-PCR revealed that SeTPS mRNA was expressed in the fat body at different developmental stages and was present at a high level in day 1 S. exigua pupae. The concentrations of trehalose and glucose in the hemolymph were determined by HPLC and showed that they varied at different developmental stages and were negatively correlated to each other. The survival rates of the insects injected with dsRNA corresponding to SeTPS gene reached 53.95%, 49.06%, 34.86% and 33.24% for 36, 48, 60 and 204h post-injection respectively which were significantly lower than those of the insects in three control groups. These findings provide new data on the tissue distribution, expression patterns and potential function of the trehalose-6-phosphate synthase gene.

Role of the C-terminal domain of Thermus thermophilus trehalose synthase in the thermophilicity, thermostability, and efficient production of trehalose

Trehalose synthase (TS) from Thermus thermophilus (TtTS) is a thermostable enzyme that catalyzes the conversion of maltose into trehalose by intramolecular transglucosylation. It has a relatively higher thermophilicity and thermostability and a better conversion ratio for trehalose production than other known TSs from different sources at present. By amino acid sequences and the schematic motif alignment of trehalose synthase-related enzymes, it was found that TtTS (965 amino acid residues) contains a particular C-terminal fragment that is not found in most other TSs. To verify the function of this fragment, C-terminal deletion and enzyme fusion were respectively performed to explain the important role this fragment plays in the formation of trehalose. First, the C terminus (TtTSDeltaN, 415 amino acid residues) of TtTS is deleted to construct a TtTSDeltaC containing 550 amino acids. Furthermore, a novel cold-active TS was cloned and purified from Deinococcus radiodurans (DrTS, 552 amino acid residues) and then a fusion protein was created with TtTSDeltaN at the C terminus of DrTS (DrTS-TtTSDeltaN). It was found that the recombinant TtTStriangle upC enzyme had a lower thermostability and a higher byproduct than TtTS in catalyzing the conversion of maltose into trehalose. On the other hand, the recombinant DrTS-TtTSDeltaN enzyme had a higher thermostability and a lower byproduct than DrTS in their reactions. The above-mentioned results allowed the inference that the C terminus of TtTS plays a key role in maintaining its thermostability and hence in modulating the side reaction to reduce glucose production at a high temperature. A new, simple, and fast method to improve thermophilicity by fusing this fragment with particular conformation to a thermolabile enzyme is offered.

Construction of a recombinant thermostable beta-amylase-trehalose synthase bifunctional enzyme for facilitating the conversion of starch to trehalose

A fusion gene that encoded a polypeptide of 1495 amino acids was constructed from the beta-amylase (BA) gene of Clostridium thermosulfurogenes and trehalose synthase (TS) gene of Thermus thermophilus. The fused gene was overexpressed in Escherichia coli, and a recombinant bifunctional fusion protein with BA at the N-terminal (BATS) or C-terminal (TSBA) of TS having both beta-amylase and trehalose synthase activities with an apparent molecular mass of 164 kDa was obtained. BATS or TSBA catalyzes the sequential reaction in which maltose is formed from starch and then is converted into trehalose. The Km values of the BATS and TSBA fusion enzymes for the reaction from starch to trehalose were smaller than those of an equimolar mixture of BA and TS (BA/TS). On the other hand, the kcat value of BATS approximated that of the BA/TS mixture, but that of TSBA exceeded it. TSBA showed much higher sequential catalytic efficiency than the separately expressed BA/TS mixture. The catalytic efficiency of TSBA or BATS was 3.4 or 2.4 times higher, respectively, than that of a mixture of individual enzymes, showing the kinetic advantage of the fusion enzyme. The thermal stability readings of the recombinant fusion enzymes BATS and TSBA were better than that of the mixture of individual recombinant enzymes. These results apparently demonstrate that fusion enzymes catalyzing sequential reactions have kinetic advantages over a mixture of both enzymes.

Laboratory-directed protein evolution

Systematic approaches to directed evolution of proteins have been documented since the 1970s. The ability to recruit new protein functions arises from the considerable substrate ambiguity of many proteins. The substrate ambiguity of a protein can be interpreted as the evolutionary potential that allows a protein to acquire new specificities through mutation or to regain function via mutations that differ from the original protein sequence. All organisms have evolutionarily exploited this substrate ambiguity. When exploited in a laboratory under controlled mutagenesis and selection, it enables a protein to "evolve" in desired directions. One of the most effective strategies in directed protein evolution is to gradually accumulate mutations, either sequentially or by recombination, while applying selective pressure. This is typically achieved by the generation of libraries of mutants followed by efficient screening of these libraries for targeted functions and subsequent repetition of the process using improved mutants from the previous screening. Here we review some of the successful strategies in creating protein diversity and the more recent progress in directed protein evolution in a wide range of scientific disciplines and its impacts in chemical, pharmaceutical, and agricultural sciences.

Mechanistic study of the intramolecular conversion of maltose to trehalose by Thermus caldophilus GK24 trehalose synthase

This paper questions what types of molecular transformation are involved in the conversion of maltose to trehalose by trehalose synthase from Thermus caldophilus GK24. The reverse reaction pathway has been examined with the aid of alpha,alpha-(2,4,6,6',2',4',6",6"'-(2)H(8))trehalose (1). The mass data of the isolated reaction products clearly indicate that deuterated glucose is confined only to substrate molecules, and thus the reversible enzymatic conversion of trehalose into maltose proceeds through an intramolecular pathway.

Directed evolution of alpha-aspartyl dipeptidase from Salmonella typhimurium

Model-free approaches (error-prone PCR to introduce random mutations, DNA shuffling to combine positive mutations, and screening of the resultant mutant libraries) have been used to enhance the catalytic activity and thermostability of alpha-aspartyl dipeptidase from Salmonella typhimurium, which is uniquely able to hydrolyze Asp-X dipeptides (where X is any amino acid) and one tripeptide (Asp-Gly-Gly). Under double selective pressures of activity and thermostability, through two rounds of error-prone PCR and three sequential generations of DNA shuffling, coupled with screening, a mutant pepEM3074 with approximately 47-fold increased enzyme activity compared with its wild-type parent was obtained. Moreover, the stability of pepEM3074 is increased significantly. Three amino acid substitutions (Asn89His, Gln153Glu, and Leu205Arg), two of them are near the active site and substrate binding pocket, were identified by sequencing the genes encoding this evolved enzyme. The mechanism of the enhancement of activity and stability was analyzed in this paper.

The trehalose myth revisited: introduction to a symposium on stabilization of cells in the dry state

This essay is an introduction to a series of papers arising from a symposium on stabilization of cells in the dry state. Nearly all of these investigations have utilized the sugar trehalose as a stabilizing molecule. Over the past two decades a myth has grown up about special properties of trehalose for stabilization of biomaterials. We review many of such uses here and show that under ideal conditions for drying and storage trehalose has few, if any, special properties. However, under suboptimal conditions trehalose has some distinct advantages and thus may remain the preferred excipient. We review the available mechanisms for introducing trehalose into the cytoplasm of living cells as an introduction to the papers that follow.