RESUMO
With the development of low-carbon economy and renewable resource, fermentation of the pentose sugar xylose to produce ethanol becomes a very hot topic. The recombinant Saccharomyces cerevisiae can be constructed by expressing heterologous xylose isomerase (XI). Because Thermus thermophilus XI (TthXI) does not need cofactor, it has been developed for establishing the utilization pathway of xylose in S. cerevisiae. In this article, we reviewed the progress on xylose isomerase. We first introduced the primary properties, sequence and structure characters of xylose isomerase, and discussed its thermostability. The molecular modification of xylose isomerase, including of substrate specificity and thermostability were discussed in detail. Meanwhile, combined with our own research, we also discussed how to improve the xylose isomerase activity at room temperature. Finally, we suggested perspectives of xylose isomerase.
Assuntos
Aldose-Cetose Isomerases , Química , Genética , Metabolismo , Catálise , Estabilidade Enzimática , Temperatura Alta , Proteínas Recombinantes , Genética , Saccharomyces cerevisiae , Genética , Metabolismo , Especificidade por SubstratoRESUMO
We used genetic methods to get a mutational spt15 gene from the recombinant strain Saccharomyces cerevisiae YPH499-3, screened by global transcription machinery engineering (gTME) approach. We transformed the gene into the original strain Saccharomyces cerevisiae YPH499 using the vector pYX212, then got a new recombinant strain. We studied the characteristic of this strain and found that it could metabolize xylose and co-ferment xylose and glucose. Under the fermentation condition of 30 degrees C, 200 r/min, 72 h, the utilization ratio of xylose was 82.0%, with 32.4% of ethanol yield when the carbon source in the media was 50 g/L xylose, while the utilization ratio of xylose and glucose was 80.4% and 100% respectively, with the 31.4% of ethanol yield when the carbon source was 50 g/L glucose/xylose (1:1). Meanwhile, the concentration of the by-product xylitol was very low. This study demonstrates the effect which the forward mutation of spt15 gene makes to the co-fermentation of xylose and glucose to ethanol by Saccharomyces cerevisiae.
Assuntos
Sequência de Bases , Etanol , Metabolismo , Engenharia Genética , Métodos , Glucose , Metabolismo , Dados de Sequência Molecular , Mutação , Saccharomyces cerevisiae , Genética , Metabolismo , Proteínas de Saccharomyces cerevisiae , Genética , Proteína de Ligação a TATA-Box , Genética , Transformação Genética , Xilose , MetabolismoRESUMO
Global transcription machinery engineering (gTME) was employed to engineer xylose metabolism. Mutation of the transcription factor gene Sptl5 was introduced by error-prone PCR, followed by screening on media using xylose as the sole carbon source. One recombinant strain growing well on such media was chosen for further research. This strain showed modest growth rates in the media containing 50 g/L xylose or glucose at the condition of 30 degrees C, 200 r/min, 96 h, 94.0% and 98.9% of xylose and glucose were consumed, with the ethanol yield were 32.4% and 31.6%, respectively. The control strain had the ethanol yield of 44.3% under the glucose concentration of 50 g/L. When the carbon source was 50 g/L glucose/xylose (1:1), the utilization ratio of xylose and glucose was 91.7% and 85.9%, with the ethanol yield was 26%. Xylose was eventually exhausted. Concentration of the by-product xylitol was very low.
Assuntos
RNA Polimerases Dirigidas por DNA , Genética , Metabolismo , Etanol , Metabolismo , Fermentação , Engenharia Genética , Métodos , Glucose , Metabolismo , Saccharomyces cerevisiae , Genética , Metabolismo , Fatores de Transcrição , Genética , Metabolismo , Transformação Genética , Xilose , MetabolismoRESUMO
RNA silencing is increasingly employed as an experimental strategy to probe for gene function in several organisms. The purpose of the present study was to test the effect of gene silencing by dsRNA in budding yeast Saccharomyces cerevisiae. GRE3 gene encoding an NADPH-dependent aldose reductase was chosen as an example. A recombinant plasmid psiLENT-GRE3 was constructed based on the pESC-LEU backbone and used to transform S. cerevisiae YPH499. The down regulation of GRE3 gene expression by inducing 1 kb RNA duplex and a 136 bp loop was investigated using reverse transcription- PCR. The results showed that double-stranded RNA mediated gene silencing could be used as a functional tool to decrease the expression level of a specific gene in S. cerevisiae, which would contribute to the understanding of RNA interference in budding yeast.