Overlapping and Distinct Roles of Aspergillus fumigatus UDP-glucose 4-Epimerases in Galactose Metabolism and the Synthesis of Galactose-containing Cell Wall Polysaccharides
Overlapping and Distinct Roles of Aspergillus fumigatus UDP-glucose 4-Epimerases in Galactose Metabolism and the Synthesis of Galactose-containing Cell Wall Polysaccharides
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DOI：
10.1074/jbc.m113.522516
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发表时间：
2014-01-17
影响因子：
4.8
通讯作者：
Sheppard, Donald C.
中科院分区：
文献类型：
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作者：
Lee, Mark J.;Gravelat, Fabrice N.;Sheppard, Donald C.
背景：烟曲霉产生两种含半乳糖的胞外多糖，半乳甘露聚糖和半乳糖胺半乳聚糖。结果：半乳糖胺半乳聚糖的合成需要UDP-葡萄糖4-差向异构酶，Uge 5和Uge 3，而半乳甘露聚糖的合成只需要Uge 5。结论：A.烟曲霉在胞外多糖合成中起着不同的和重叠的作用。重要性：揭示半乳糖胺半乳聚糖的生物合成途径将是开发针对这种胞外多糖的治疗方法的关键。烟曲霉的细胞壁含有两种含半乳糖的多糖，半乳甘露聚糖和半乳糖胺半乳聚糖，其生物合成途径还不清楚。助理烟曲霉基因组含有编码推定的UDP-葡萄糖4-差向异构酶的三个基因，uge 3、uge 4和uge 5。我们进行了这项研究，以阐明这些差向异构酶的功能。我们发现，uge 4是最低限度的表达，并不需要含半乳糖的胞外多糖或半乳糖代谢的合成。Uge 5是A.是烟曲霉的主要生长因子，并且是在半乳糖基培养基中正常生长所必需的。Uge 5是合成半乳甘露聚糖的半乳糖呋喃糖（Galf）组分所必需的，并为半乳糖胺半乳聚糖的合成提供半乳糖。Uge 3可以介导UDP-半乳糖和UDP-N-乙酰半乳糖胺（GalNAc）的产生，并且是半乳糖胺半乳聚糖而不是半乳甘露聚糖产生所需的。在不存在Uge 5的情况下，Uge 3活性足以在半乳糖上生长和合成含有较低水平半乳糖的半乳糖胺半乳聚糖，但不足以合成Galf。Uge 5和Uge 3的双缺失阻断了半乳糖的生长以及Galf和半乳糖胺半乳聚糖的合成。本研究首次对A. fumigatus和有助于我们了解这些酶在代谢和细胞壁合成中的作用。
Background:Aspergillus fumigatus produces two galactose-containing exopolysaccharides, galactomannan and galactosaminogalactan. Results: Galactosaminogalactan synthesis requires the UDP-glucose 4-epimerases, Uge5 and Uge3, whereas galactomannan synthesis requires Uge5 alone. Conclusion: Epimerases in A. fumigatus play both distinct and overlapping roles in exopolysaccharide synthesis. Significance: Uncovering the biosynthetic pathways of galactosaminogalactan will be crucial in developing therapeutics targeting this exopolysaccharide.The cell wall of Aspergillus fumigatus contains two galactose-containing polysaccharides, galactomannan and galactosaminogalactan, whose biosynthetic pathways are not well understood. The A. fumigatus genome contains three genes encoding putative UDP-glucose 4-epimerases, uge3, uge4, and uge5. We undertook this study to elucidate the function of these epimerases. We found that uge4 is minimally expressed and is not required for the synthesis of galactose-containing exopolysaccharides or galactose metabolism. Uge5 is the dominant UDP-glucose 4-epimerase in A. fumigatus and is essential for normal growth in galactose-based medium. Uge5 is required for synthesis of the galactofuranose (Galf) component of galactomannan and contributes galactose to the synthesis of galactosaminogalactan. Uge3 can mediate production of both UDP-galactose and UDP-N-acetylgalactosamine (GalNAc) and is required for the production of galactosaminogalactan but not galactomannan. In the absence of Uge5, Uge3 activity is sufficient for growth on galactose and the synthesis of galactosaminogalactan containing lower levels of galactose but not the synthesis of Galf. A double deletion of uge5 and uge3 blocked growth on galactose and synthesis of both Galf and galactosaminogalactan. This study is the first survey of glucose epimerases in A. fumigatus and contributes to our understanding of the role of these enzymes in metabolism and cell wall synthesis.