Iosue Christine L, Attanasio Nicholas, Shaik Noor F, Neal Erin M, Leone Sarah G, Cali Brian J, Peel Michael T, Grannas Amanda M, Wykoff Dennis D
Department of Biology, Villanova University, Villanova, Pennsylvania, United States of America.
Department of Chemistry, Villanova University, Villanova, Pennsylvania, United States of America.
PLoS One. 2016 Mar 25;11(3):e0152042. doi: 10.1371/journal.pone.0152042. eCollection 2016.
The phosphorylated form of thiamine (Vitamin B1), thiamine pyrophosphate (TPP) is essential for the metabolism of amino acids and carbohydrates in all organisms. Plants and microorganisms, such as yeast, synthesize thiamine de novo whereas animals do not. The thiamine signal transduction (THI) pathway in Saccharomyces cerevisiae is well characterized. The ~10 genes required for thiamine biosynthesis and uptake are transcriptionally upregulated during thiamine starvation by THI2, THI3, and PDC2. Candida glabrata, a human commensal and opportunistic pathogen, is closely related to S. cerevisiae but is missing half of the biosynthetic pathway, which limits its ability to make thiamine. We investigated the changes to the THI pathway in C. glabrata, confirming orthologous functions. We found that C. glabrata is unable to synthesize the pyrimidine subunit of thiamine as well as the thiamine precursor vitamin B6. In addition, THI2 (the gene encoding a transcription factor) is not present in C. glabrata, indicating a difference in the transcriptional regulation of the pathway. Although the pathway is upregulated by thiamine starvation in both species, C. glabrata appears to upregulate genes involved in thiamine uptake to a greater extent than S. cerevisiae. However, the altered regulation of the THI pathway does not alter the concentration of thiamine and its vitamers in the two species as measured by HPLC. Finally, we demonstrate potential consequences to having a partial decay of the THI biosynthetic and regulatory pathway. When the two species are co-cultured, the presence of thiamine allows C. glabrata to rapidly outcompete S. cerevisiae, while absence of thiamine allows S. cerevisiae to outcompete C. glabrata. This simplification of the THI pathway in C. glabrata suggests its environment provides thiamine and/or its precursors to cells, whereas S. cerevisiae is not as reliant on environmental sources of thiamine.
硫胺素（维生素B1）的磷酸化形式，即硫胺素焦磷酸（TPP），对所有生物体中氨基酸和碳水化合物的代谢至关重要。植物和微生物，如酵母，能从头合成硫胺素，而动物则不能。酿酒酵母中的硫胺素信号转导（THI）途径已得到充分表征。硫胺素生物合成和摄取所需的约10个基因在硫胺素饥饿期间被THI2、THI3和PDC2转录上调。光滑念珠菌是一种人体共生菌和机会致病菌，与酿酒酵母密切相关，但缺少一半的生物合成途径，这限制了其合成硫胺素的能力。我们研究了光滑念珠菌中THI途径的变化，证实了其直系同源功能。我们发现光滑念珠菌无法合成硫胺素的嘧啶亚基以及硫胺素前体维生素B6。此外，光滑念珠菌中不存在THI2（编码转录因子的基因），这表明该途径的转录调控存在差异。尽管在这两个物种中，该途径在硫胺素饥饿时都会上调，但光滑念珠菌似乎比酿酒酵母更能上调参与硫胺素摄取的基因。然而，通过高效液相色谱法测定，THI途径调控的改变并未改变这两个物种中硫胺素及其维生素变体的浓度。最后，我们证明了THI生物合成和调控途径部分衰退的潜在后果。当这两个物种共培养时，硫胺素的存在使光滑念珠菌能够迅速胜过酿酒酵母，而硫胺素的缺失则使酿酒酵母能够胜过光滑念珠菌。光滑念珠菌中THI途径的这种简化表明其环境为细胞提供了硫胺素和/或其前体，而酿酒酵母对硫胺素的环境来源依赖性较小。
