Biology subjects

Xiu, Y.

Publications and source records attributed to Xiu, Y..

3 recordsLinked to original sources

bioRxiv2022

Reduced methionine synthase (Mtr) expression creates a functional vitamin B12 deficiency that leads to uracil accumulation in mouse mitochondrial DNA

Adequate thymidylate (dTMP or the "T" base in DNA) levels are essential for stability of mitochondrial DNA (mtDNA) and nuclear DNA (nDNA). Folate and vitamin B12 (B12) are essential cofactors in folate-mediated one carbon metabolism (FOCM), a metabolic network which supports synthesis of nucleotides (including dTMP) and methionine. Perturbations in FOCM impair dTMP synthesis, causing misincorporation of uracil (or a "U" base) into DNA. During B12 deficiency, cellular folate accumulates as 5-methyltetrahdryfolate (5-methyl-THF), limiting nucleotide synthesis. The purpose of this study was to determine how B12 deficiency and dietary folate interact to affect mtDNA integrity and mitochondrial function in mouse liver. Mice expressing reduced methionine synthase (Mtr) levels were used to create a functional B12 deficiency. Folate accumulation, uracil levels, mtDNA content, and oxidative phosphorylation capacity were measured in male Mtr+/+ and Mtr+/- mice weaned onto either a folate-sufficient control diet (2 mg/kg folic acid, C) or a folate-deficient diet (FD, lacking folic acid) for 7 weeks. Mtr heterozygosity led to increased liver 5-methyl-THF levels. Mtr+/- mice consuming the C diet also exhibited a 40-fold increase in uracil in liver mtDNA. However, the combination of Mtr heterozygosity and exposure to the FD diet partially alleviated the level of uracil accumulation in mtDNA. Furthermore, Mtr+/- mice exhibited a 25% decrease in liver mtDNA content and a 20% decrease in maximal oxygen consumption rates. Impairments in mitochondrial FOCM are known to lead to increased uracil in mtDNA. This study demonstrates that impaired cytosolic dTMP synthesis also leads to increased uracil in mtDNA.

biochemistry↗

bioRxiv2022

Structural and functional insights into the type III-E CRISPR-Cas immunity

The type III-E CRISPR-Cas system comprises a Cas effector (gRAMP), a TPR-CHAT and several ancillary proteins. However, both the structural features of gRAMP and the immunity mechanism remain unknown for this system. Here, we report a series of structures of gRAMP-crRNA, either its alone or in complex with target RNA or TPR-CHAT (called Craspase), and Craspase complexed with cognate (CTR) or non-cognate target RNA (NTR). Importantly, the 3 anti-tag region of NTR and CTR bind at two distinct channels in the Craspase, and CTR with a non-complementary 3 anti-tag induces a marked conformational change of the TPR-CHAT, which allosterically activates its protease activity to cleave an ancillary protein Csx30. This cleavage then triggers an abortive infection as the antiviral strategy of the type III-E system. Together, our study provides crucial insights into both the catalytic mechanism of the gRAMP and the immunity mechanism of the type III-E CRISPR-Cas system.

molecular biology↗

bioRxiv2021

Reduced Shmt2 expression impairs mitochondrial folate accumulation and respiration, and leads to uracil accumulation in mouse mitochondrial DNA

BackgroundAdequate cellular thymidylate (dTMP) pools are essential for preservation of nuclear and mitochondrial genome stability. Previous studies have indicated that disruption in dTMP synthesis in the nucleus leads to increased uracil misincorporation into DNA affecting genome stability. To date, the effects of impaired mitochondrial dTMP synthesis in non- transformed tissues have been understudied. ObjectiveThis study aimed to determine the effects of decreased serine hydroxymethyltransferase 2 (Shmt2) expression and dietary folate deficiency on mitochondrial DNA integrity and mitochondrial function in mouse tissues. MethodsLiver mitochondrial DNA (mtDNA) content, and uracil content in liver mtDNA was measured in Shmt2+/- and Shmt2+/+ mice weaned onto either a folate-sufficient control diet (2 mg/kg folic acid, C) or a modified diet lacking folic acid (0 mg/kg folic acid, FD) for 7 wks. Shmt2+/- and Shmt2+/+ mouse embryonic fibroblasts (MEF cells) were cultured in defined culture medium containing either 0 or 25 nM folate to assess proliferative capacity and mitochondrial function. ResultsShmt2+/- mice exhibited 48-67% reduction in SHMT2 protein levels in tissues. Interestingly, Shmt2+/- mice consuming the folate-sufficient C diet exhibited a 25% reduction in total folate in liver mitochondria. There was also a >20-fold increase in uracil in liver mtDNA in Shmt2+/- mice consuming the C diet, and dietary folate deficiency also increased uracil content in mouse liver mtDNA from both Shmt2+/+ and Shmt2+/- mice. Furthermore, decreased Shmt2 expression in MEF cells reduced cell proliferation, mitochondrial membrane potential, and oxygen consumption rate. ConclusionsThis study demonstrates that Shmt2 heterozygosity and dietary folate deficiency impair mitochondrial dTMP synthesis, as evidenced by the increased uracil in mtDNA. In addition, Shmt2 heterozygosity impairs mitochondrial function in MEF cells. These findings suggest that elevated uracil in mtDNA may impair mitochondrial function.

biochemistry↗