8-Hydroxyguanine,A Product From Damaged DNA Can Be Used in the DNA Salvage Pathways

The metabolic mechanism of 8-hydroxyguanine (8-OHGua) is so far unknown, however it is known to function in the mutagenic events in biological systems. In the present study, the metabolic processes is investigated by the reaction of 8-OHGua with PRPP catalyzed by HGPRT and Mg(II). The evidence shows that the interaction between 8-OHGua and the enzyme is indeed taken place and 8-OHGMP is formed.

Construction of an engineered Escherichia coli for effective synthesis of 2'-fucosyllactose via the salvage pathway

2'-Fucosyllactose(2'-FL)is one of the important functional oligosaccharides in breast milk.So far,few attempts on biosynthesis of 2'-FL by the salvage pathway have been reported.Herein,the salvage pathway enzyme genes were introduced into the E.coli BL21star(DE3)for synthesis of 2'-FL.The 2'-FL titer increased from 1.56 to 2.13 g/L by deleting several endogenous genes on competitive pathways.Theα-1,2-fucosyltransferase(WbgL)was selected,and improved the 2'-FL titer to 2.88 g/L.Additionally,the expression level of pathway enzyme genes was tuned through optimizing the plasmid copy number.Furthermore,the spatial distribution of WbgL was enhanced by fusing with the MinD C-tag.After optimizing the fermentation conditions,the 2'-FL titer reached to 7.13 g/L.The final strain produced 59.22 g/L of 2'-FL with 95%molar conversion rate of lactose and 92% molar conversion rate of fucose in a 5 L fermenter.These findings will contribute to construct a highly efficient microbial cell factory to produce 2'-FL or other HMOs.

Improved Growth and Stress Tolerance in the Arabidopsis oxtl Mutant Triggered by Altered Adenine Metabolism

Plants perceive and respond to environmental stresses with complex mechanisms that are often associ- ated with the activation of antioxidant defenses. A genetic screen aimed at isolating oxidative stress-tolerant lines of Arabidopsis thaliana has identified oxtl, a line that exhibits improved tolerance to oxidative stress and elevated temperature but displays no apparent deleterious growth effects under non-stress conditions. Oxtl harbors a muta- tion that arises from the altered expression of a gene encoding adenine phosphoribosyltransferase （APT1）, an enzyme that converts adenine to adenosine monophosphate （AMP）, indicating a link between purine metabolism, whole-plant growth responses, and stress acclimation. The oxtl mutation results in decreased APT1 expression that leads to reduced enzymatic activity. Correspondingly, oxtl plants possess elevated levels of adenine. Decreased APT enzyme activity dir- ectly correlates with stress resistance in transgenic lines that ectopically express APT1. The metabolic alteration in oxtl plants also alters the expression of several antioxidant defense genes and the response of these genes to oxidative chal- lenge. Finally, it is shown that manipulation of adenine levels can induce stress tolerance to wild-type plants. Collectively, these results show that alterations in cellular adenine levels can trigger stress tolerance and improve growth, leading to increases in plant biomass. The results also suggest that adenine might play a part in the signals that modulate responses to abiotic stress and plant growth.

Non-Viral Deoxyribonucleoside Kinases——Diversity and Practical Use

Deoxyribonucleoside kinases （dNKs） phosphorylate deoxyribonucleosides to their corresponding monophosphate compounds, dNks also phosphorylate deoxyribonucleoside analogues that are used in the treatment of cancer or viral infections. The study of the mammalian dNKs has therefore always been of great medical interest. However, during the last 20 years, research on dNKs has gone into non- mammalian organisms. In this review, we focus on non-viral dNKs, in particular their diversity and their practical applications. The diversity of this enzyme family in different organisms has proven to be valuable in studying the evolution of enzymes. Some of these newly discovered enzymes have been useful in numerous practical applications in medicine and biotechnology, and have contributed to our understanding of the structural basis of nucleoside and nucleoside analogue activation.