The chitin catabolic cascade in the marine bacterium Vibrio cholerae:: Characterization of a unique chitin oligosaccharide deacetylase
The chitin catabolic cascade in the marine bacterium Vibrio cholerae:: Characterization of a unique chitin oligosaccharide deacetylase
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DOI：
10.1093/glycob/cwm096
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发表时间：
2007-12-01
期刊：
影响因子：
4.3
通讯作者：
Roseman, Saul
中科院分区：
文献类型：
--
作者：
Li, Xibing;Wang, Lai-Xi;Roseman, Saul
甲壳素是自然界中最丰富的有机物质之一，其被海洋细菌（例如霍乱弧菌）通过大量严格调控的基因消耗（Li和Roseman 2004，Proc Natl Acad Sci USA. 101：627631）。其中一个这样的基因，鳕鱼，在这里报道。当细胞被壳二糖、（GlcNH（2））（2）或粗制蟹壳诱导时，它编码一种壳寡糖脱乙酰酶（COD）。COD被分子克隆（COD-6 His），过度生产，并纯化至明显的同质性。COD在诱导的霍乱弧菌生长的所有阶段都有分泌。该基因序列预测的26个N-末端氨基酸的信号肽中没有发现的分离的蛋白质。COD对甲壳质寡糖非常有活性，对GlcNAc几乎没有活性，对胶体（H-3-N-乙酰基）-甲壳质有轻微活性。低聚糖几乎定量地转化为缺少一个乙酰基的产物。后者通过质谱（ESI-MS）和亚硝酸处理进行表征。COD催化下列反应（n = 2-6）：（GlcNAc）（n）-> GlcNAc-GlcNH（2-）（GlcNAc）（n-2）+ Ac-。也就是说，COD水解与倒数第二个GlcNAc残基连接的N-乙酰基。基因库序列数据显示cod在弧菌属和发光菌属中高度保守。一种这样的基因编码从溶藻弧菌分离的脱乙酰酶（Ohishi等，1997，Biosci Biotech Biochem.61：1113 - 1117; Ohishi等，2000，J Biosci Bioeng. 90：561563），其对（GlcNAc）（2）具有特异性，但对更高的寡糖无活性。COD酶促产物GlcNAc-GlcNH（2）-（GlcNAc）（n）与用Nod B：GlcNH（2）-（GlcNAc）（3-4）水解壳寡糖获得的产物非常相似。后者是结瘤因子生物合成的关键中间体，在共生固氮细菌和植物之间的通讯中至关重要。可以想象，COD产品在蜂窝通信中发挥着同样重要的作用，但仍有待定义。
Chitin, one of the most abundant organic substances in nature, is consumed by marine bacteria, such as Vibrio cholerae, via a multitude of tightly regulated genes (Li and Roseman 2004, Proc Natl Acad Sci USA. 101:627631). One such gene, cod, is reported here. It encodes a chitin oligosaccharide deacetylase (COD), when cells are induced by chitobiose, (GlcNH(2))(2), or crude crab shells. COD was molecularly cloned (COD-6His), overproduced, and purified to apparent homogeneity. COD is secreted at all stages of growth by induced V. cholerae. The gene sequence predicts a 26 N-terminal amino acid signal peptide not found in the isolated protein. COD is very active with chitin oligosaccharides, is virtually inactive with GlcNAc, and slightly active with colloidal (H-3-N-acetyl)-chitin. The oligosaccharides are converted almost quantitatively to products lacking one acetyl group. The latter were characterized by mass spectrometry (ESI-MS), and treatment with nitrous acid. COD catalyzes the following reactions (n = 2-6): (GlcNAc)(n) -> GlcNAc-GlcNH(2-)(GlcNAc)(n-2) + Ac-. That is, COD hydrolyzes the N-acetyl groups attached to the penultimate GlcNAc residue. The gene bank sequence data show that cod is highly conserved in Vibrios and Photobacteria. One such gene encodes a deacetylase isolated from V. alginolytics (Ohishi et al. 1997, Biosci Biotech Biochem. 61:11131117; Ohishi et al. 2000, J Biosci Bioeng. 90:561563), that is specific for (GlcNAc)(2), but inactive with higher oligosaccharides. The COD enzymatic products, GlcNAc-GlcNH(2)-(GlcNAc)(n), closely resemble those obtained by hydrolysis of the chitooligosaccharides with Nod B: GlcNH(2)-(GlcNAc)(3-4). The latter are key intermediates in the biosynthesis of Nod factors, critically important in communications between the symbiotic nitrogen fixing bacteria and plants. Conceivably, the COD products play equally important roles in cellular communications that remain to be defined.