Uv-induced DNA Damage Repair Facilitated By Pentose Phospate Pathway In Deinococcus Radiodurans

Deinococcus radiodurans is characterized by its extreme resistance to ionizing radiation, desiccation, ultraviolet (UV), and other DNA damaging agents. The pentose phosphate pathway (PPP) plays a crucial role in cellular carbon metabolism. D-ribose-5-phosphate and NADPH are intermediates of PPP, providing substrates and energy for DNA damage repair mechanisms. However, a cell's mechanism of UV resistance and DNA repair of PPP in D. radiodurans remain obscure.PPP is essential for an organism, but preliminary findings on PPP in D. radiodurans focused mainly on its first enzyme, glucose 6-phosphate dehydrogenase (G6PD, zwf). In this study, the G6PD-deficient mutant (?zwf), transaldolase(TAL)-deficient mutant (?tal), and transketolase(TKT) heterozygous mutant (?tkt) were constructed by homologous recombination. The ?tkt strain grew more slowly and utilized fewer types of carbohydrates as its sole carbon source compared to the wild type. Additionally, it was more sensitive to UV irradiation. Growth was not affected in the G6PDH and TAL-deficient mutants while theΔzwf strain showed slightly more sensitivity to UV irradiation.The amounts of D-ribose and NADPH in three mutants and transcriptional level changes of some important genes in PPP, NER, MMR, and other metabolic pathways were assayed before and after 10 min of UV irradiation. Results before UV treatment showed that the amount of D-ribose and NADPH were unchanged inΔtal compared to the wild type. The D-ribose content inΔzwf was lower than that of the wild type and the NADPH content was unchanged. In the tkt- incompletely deficient mutant, cellular levels of D-ribose and NADPH were higher compared to the wild type. Transcriptional level variations of genes encoding for enzymes involved in excision repair, PPP, EMP, and SAP were analyzed. There were no changes in the transcriptional levels of these genes inΔzwf andΔtal. However, the transcriptional level of genes encoding for enzymes in PPP was increased inΔtkt. These results indicated that tkt plays a greater role in PPP. After being treated with UV irradiation for 10 min, the zwf-mutant had a lower content of D-ribose and NADPH than the wild type. The expression of genes involved in PPP, EMP, SAP, NER and MMR was slightly up-regulated. The amount of D-ribose inΔtkt increased, but NADPH content decreased compared to the wild type. The expression of important genes in PPP, EMP, SAP, NER, and MMR increased observably. InΔtal, there were no changes except for an increase in D-ribose content compared to the wild type.Although tal-deficiency led to an increase in cellular D-ribose, UV-resistance was not modified greatly. In the zwf and tkt mutants, the expression of genes in NER, MMR, and other pathways increased and cellular NADPH content decreased. Cellular D-ribose content increased inΔtkt, but the opposite was true inΔzwf. Results suggested that variation of cellular NADPH levels is relevant to the strain's phenotype of UV-resistance.In conclusion, zwf and tkt deficiencies affect growth, UV-resistance, and transcriptional levels of some crucial genes. G6PDH and TKT are key enzymes in PPP in D. radiodurans. An intermediate metabolite, NADPH,is generated which is the most important reducing agent and plays a large role in regulating UV induced cellular damage repair by PPP.