Department of Bioscience and Biotechnology, Graduate School of Bioresource and Bioenvironmental Sciences, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan.
Department of Metabolome, Graduate School of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan; Institute for Advanced Biosciences, Keio University, 246-2 Mizukami, Kakuganji, Tsuruoka, Yamagata 997-0052, Japan.
J Biol Chem. 2012 Jan 2;287(1):368-381. doi: 10.1074/jbc.M111.311340. Epub 2011 Nov 9.
A fungus-specific glucosylceramide (GlcCer), which contains a unique sphingoid base possessing two double bonds and a methyl substitution, is essential for pathogenicity in fungi. Although the biosynthetic pathway of the GlcCer has been well elucidated, little is known about GlcCer catabolism because a GlcCer-degrading enzyme (glucocerebrosidase) has yet to be identified in fungi. We found a homologue of endoglycoceramidase tentatively designated endoglycoceramidase-related protein 1 (EGCrP1) in several fungal genomic databases. The recombinant EGCrP1 hydrolyzed GlcCer but not other glycosphingolipids, whereas endoglycoceramidase hydrolyzed oligosaccharide-linked glycosphingolipids but not GlcCer. Disruption of egcrp1 in Cryptococcus neoformans, a typical pathogenic fungus causing cryptococcosis, resulted in the accumulation of fungus-specific GlcCer and immature GlcCer that possess sphingoid bases without a methyl substitution concomitant with a dysfunction of polysaccharide capsule formation. These results indicated that EGCrP1 participates in the catabolism of GlcCer and especially functions to eliminate immature GlcCer in vivo that are generated as by-products due to the broad specificity of GlcCer synthase. We conclude that EGCrP1, a glucocerebrosidase identified for the first time in fungi, controls the quality of GlcCer by eliminating immature GlcCer incorrectly generated in C. neoformans, leading to accurate processing of fungus-specific GlcCer.
真菌特有的葡糖基神经酰胺（GlcCer）含有一个独特的神经酰胺碱基，具有两个双键和一个甲基取代基，对于真菌的致病性是必不可少的。尽管 GlcCer 的生物合成途径已经得到很好的阐明，但由于尚未在真菌中鉴定出 GlcCer 降解酶（葡糖脑苷脂酶），因此对 GlcCer 分解代谢知之甚少。我们在几个真菌基因组数据库中发现了一种内切葡糖神经酰胺酶的同源物，暂定名为内切葡糖神经酰胺酶相关蛋白 1（EGCrP1）。重组 EGCrP1 水解 GlcCer，但不水解其他糖脂，而内切葡糖脑苷脂酶水解糖链连接的糖脂，但不水解 GlcCer。在新型隐球菌（一种引起隐球菌病的典型致病性真菌）中敲除 egcrp1 导致真菌特异性 GlcCer 和缺乏甲基取代的不成熟 GlcCer 积累，同时多糖荚膜形成功能障碍。这些结果表明 EGCrP1 参与 GlcCer 的分解代谢，特别是在体内消除由于 GlcCer 合酶的广泛特异性而产生的作为副产物的不成熟 GlcCer。我们得出结论，EGCrP1 是首次在真菌中鉴定出的葡糖脑苷脂酶，通过消除新型隐球菌中错误生成的不成熟 GlcCer 来控制 GlcCer 的质量，从而导致真菌特异性 GlcCer 的准确加工。
