Clostridium thermocellum cellulosomal genes are regulated by extracytoplasmic polysaccharides via alternative sigma factors
Clostridium thermocellum cellulosomal genes are regulated by extracytoplasmic polysaccharides via alternative sigma factors
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DOI：
10.1073/pnas.1012175107
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发表时间：
2010-10-26
影响因子：
11.1
通讯作者：
Shoham, Yuval
中科院分区：
文献类型：
--
作者：
Nataf, Yakir;Bahari, Liat;Shoham, Yuval
热纤梭菌产生高效的纤维素分解胞外复合物，称为纤维素体，用于水解植物细胞壁生物质。多纤维素酶体的组成受胞外多糖的影响;然而，其调节机制尚不清楚。最近，我们在C.热纤维素是一组推定的σ和反σ因子，其包括胞外多糖传感组分[Kahel-Raifer等人（2010）FEMS Microbiol Lett 308：84-93]。这些因子编码基因与枯草芽孢杆菌双顺反子操纵子sigI-rsgI同源，后者编码另一种s I因子及其同源反sigma（1）调节因子RsgI，后者在功能上受胞质外信号调节。在本研究中，C。测定了热纤蛋白推定的抗-s I因子对其相应的s因子的结合特异性和解离常数，其范围为0.02至1 μ M。定量实时RT-PCR测量结果显示，在纤维素和木聚糖的存在下，替代s因子基因的表达增加了3至30倍，从而将其表达与其胞外多糖底物的直接检测相连接。基于启动子的序列相似性，鉴定了受这两种s因子sigma（I1）或sigma（I6）调控的纤维素体基因。通过径流转录测定在体外证明了sigI（I1）指导sigI 1启动子和celS启动子（编码家族48纤维素酶）转录的能力。两者合计，结果揭示了一种调节机制，其中替代S因子参与调节cellulosomal基因通过外部碳水化合物传感机制。
Clostridium thermocellum produces a highly efficient cellulolytic extracellular complex, termed the cellulosome, for hydrolyzing plant cell wall biomass. The composition of the cellulosome is affected by the presence of extracellular polysaccharides; however, the regulatory mechanism is unknown. Recently, we have identified in C. thermocellum a set of putative sigma and anti-sigma s factors that include extracellular polysaccharide-sensing components [Kahel-Raifer et al. (2010) FEMS Microbiol Lett 308:84-93]. These factor-encoding genes are homologous to the Bacillus subtilis bicistronic operon sigI-rsgI, which encodes for an alternative s I factor and its cognate anti-sigma(1) regulator RsgI that is functionally regulated by an extracytoplasmic signal. In this study, the binding of C. thermocellum putative anti-s I factors to their corresponding s factors was measured, demonstrating binding specificity and dissociation constants in the range of 0.02 to 1 mu M. Quantitative real-time RT-PCR measurements revealed three-to 30-fold up-expression of the alternative s factor genes in the presence of cellulose and xylan, thus connecting their expression to direct detection of their extracellular polysaccharide substrates. Cellulosomal genes that are putatively regulated by two of these s factors, sigma(I1) or sigma(I6), were identified based on the sequence similarity of their promoters. The ability of sigma(I1) to direct transcription from the sigI1 promoter and from the promoter of celS (encodes the family 48 cellulase) was demonstrated in vitro by runoff transcription assays. Taken together, the results reveal a regulatory mechanism in which alternative s factors are involved in regulating the cellulosomal genes via an external carbohydrate-sensing mechanism.