Molecular Biotechnology, Research Division Biochemical Technology, Institute of Chemical, Environmental and Biological Engineering, TU Wien, Vienna, Austria.
Fungal Physiology, Westerdijk Fungal Biodiversity Institute & Fungal Molecular Physiology, Utrecht University, Utrecht, The Netherlands.
Fungal Genet Biol. 2017 Oct;107:1-11. doi: 10.1016/j.fgb.2017.07.005. Epub 2017 Jul 20.
N-acetylglucosamine (GlcNAc) is the monomer of the polysaccharide chitin, an essential structural component of the fungal cell wall and the arthropod exoskeleton. We recently showed that the genes encoding the enzymes for GlcNAc catabolism are clustered in several ascomycetes. In the present study we tested these fungi for growth on GlcNAc and chitin. All fungi, containing the GlcNAc gene cluster, could grow on GlcNAc with the exception of four independent Neurospora crassa wild-type isolates, which were however able to grow on chitin. GlcNAc even inhibited their growth in the presence of other carbon sources. Genes involved in GlcNAc catabolism were strongly upregulated in the presence of GlcNAc, but during growth on chitin their expression was not increased. Deletion of hxk-3 (encoding the first catabolic enzyme, GlcNAc-hexokinase) and ngt-1 (encoding the GlcNAc transporter) improved growth of N. crassa on GlcNAc in the presence of glycerol. A crucial step in GlcNAc catabolism is enzymatic conversion from glucosamine-6-phosphate to fructose-6-phosphate, catalyzed by the glucosamine-6-phosphate deaminase, DAM-1. To assess, if DAM-1 is compromised in N. crassa, the orthologue from Trichoderma reesei, Trdam1, was expressed in N. crassa. Trdam1 expression partially alleviated the negative effects of GlcNAc in the presence of a second carbon source, but did not fully restore growth on GlcNAc. Our results indicate that the GlcNAc-catabolism pathway is bypassed during growth of N. crassa on chitin by use of an alternative pathway, emphasizing the different strategies that have evolved in the fungal kingdom for chitin utilization.
N-乙酰葡萄糖胺（GlcNAc）是多糖几丁质的单体，是真菌细胞壁和节肢动物外骨骼的重要结构成分。我们最近表明，编码 GlcNAc 分解代谢酶的基因在几个子囊菌中聚集在一起。在本研究中，我们测试了这些真菌对 GlcNAc 和几丁质的生长。除了四个独立的粗糙脉孢菌野生型分离株外，所有含有 GlcNAc 基因簇的真菌都可以在 GlcNAc 上生长，而这四个独立的粗糙脉孢菌野生型分离株则可以在几丁质上生长。GlcNAc 甚至在存在其他碳源的情况下抑制它们的生长。在 GlcNAc 存在下，参与 GlcNAc 分解代谢的基因被强烈上调，但在几丁质上生长时其表达没有增加。Hxk-3（编码第一分解代谢酶，GlcNAc-己糖激酶）和 Ngt-1（编码 GlcNAc 转运蛋白）的缺失改善了 N. crassa 在甘油存在下 GlcNAc 的生长。GlcNAc 分解代谢的关键步骤是由葡萄糖胺-6-磷酸酶催化，将葡萄糖胺-6-磷酸转化为果糖-6-磷酸。为了评估 N. crassa 中的 DAM-1 是否受损，我们在 N. crassa 中表达了来自里氏木霉的同源物 Trdam1。Trdam1 的表达部分缓解了 GlcNAc 在存在第二种碳源时的负面影响，但并未完全恢复 N. crassa 对 GlcNAc 的生长。我们的结果表明，在 N. crassa 生长几丁质时，GlcNAc 分解代谢途径被绕过，通过使用替代途径，强调了真菌界中为利用几丁质而进化出的不同策略。
