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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >The chitinolytic cascade in Vibrios is regulated by chitin oligosaccharides and a two-component chitin catabolic sensor/kinase
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The chitinolytic cascade in Vibrios is regulated by chitin oligosaccharides and a two-component chitin catabolic sensor/kinase

机译：弧菌中的几丁质分解反应受几丁质寡糖和两组分几丁质分解代谢传感器/激酶的调节

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摘要

Chitin, a highly insoluble polymer of GlcNAc, is produced in massive quantities in the marine environment. Fortunately for survival of aquatic ecosystems, chitin is rapidly catabolized by marine bacteria. Here we describe a bacterial two-component hybrid sensor/ kinase (of the ArcB type) that rigorously controls expression of ≈50 genes, many involved in chitin degradation. The sensor gene, chiS, was identified in Vibrio furnissii and Vibrio cholerae (predicted amino acid sequences, full-length: 84% identical, 93% similar). Mutants of chiS grew normally on GlcNAc but did not express extracellular chitinase, a specific chitoporin, or β-hexosaminidases, nor did they exhibit chemotaxis, transport, or growth on chitin oligosaccharides such as (GlcNAc)_2. Expression of these systems requires three components: wild-type chiS; a periplasmic high-affinity chitin oligosaccharide, (GlcNAc)_n (n > 1), binding protein (CBP); and the environmental signal, (GlcNAc)_n. Our data are consistent with the following model. In the uninduced state, CBP binds to the periplasmic domain of ChiS and "locks" it into the minus conformation. The environmental signal, (GlcNAc)_n, dissociates the complex by binding to CBP, releasing ChiS, yielding the plus phenotype (expression of chitinolytic genes). In V. cholerae, a cluster of 10 contiguous genes (VC0620-VC0611) apparently comprise a (GlcNAc)_2 catabolic operon. CBP is encoded by the first, VC0620, whereas VC0619-VC0616 encode a (GlcNAc)_2 ABC-type permease. Regulation of chiS requires expression of CBP but not (GlcNAc)_2 transport. (GlcNAc)_n is suggested to be essential for signaling these cells that chitin is in the microenvironment.
机译：几丁质是GlcNAc的高度不溶性聚合物，在海洋环境中大量生产。幸运的是，对于水生生态系统的生存，几丁质被海洋细菌迅速分解代谢。在这里，我们描述了一种细菌两组分混合传感器/激酶（ArcB型），它严格控制≈50个基因的表达，其中许多基因参与甲壳质的降解。在弗氏弧菌和霍乱弧菌中鉴定了传感器基因chiS（预测的氨基酸序列，全长：84％相同，93％相似）。 chiS突变体在GlcNAc上正常生长，但不表达胞外几丁质酶，特定的壳蛋白或β-己糖胺酶，也不在（GlcNAc）_2等几丁质寡糖上表现出趋化性，转运或生长。这些系统的表达需要三个组成部分：野生型chiS；周质高亲和力几丁质寡糖（GlcNAc）_n（n> 1）结合蛋白（CBP）;和环境信号（GlcNAc）_n。我们的数据与以下模型一致。在未诱导状态下，CBP与ChiS的周质结构域结合，并将其“锁定”为负构象。环境信号（GlcNAc）_n通过与CBP结合而解离复合物，释放ChiS，从而产生正表型（表达几丁质分解基因）。在霍乱弧菌中，由10个连续基因（VC0620-VC0611）组成的簇显然包含（GlcNAc）_2分解代谢操纵子。 CBP由第一个VC0620编码，而VC0619-VC0616编码（GlcNAc）_2 ABC型渗透酶。 chiS的调节需要表达CBP，但不需要（GlcNAc）_2转运。建议（GlcNAc）_n对于向这些细胞发出几丁质存在于微环境中的信号至关重要。

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