Saito Akihiro, Fujii Takeshi, Shinya Tomonori, Shibuya Naoto, Ando Akikazu, Miyashita Kiyotaka
Graduate School of Advanced Integration Science, Chiba University, Matsudo 648, Matsudo City, Chiba 271-8510, Japan.
National Institute of Agro-Environmental Sciences, Kannondai 3-1-1, Tsukuba, Ibaraki 305-8604, Japan.
Microbiology (Reading). 2008 Nov;154(Pt 11):3358-3365. doi: 10.1099/mic.0.2008/019612-0.
The dasABC genes encode an ATP-binding cassette (ABC) transporter, which is one of the uptake systems for N,N'-diacetylchitobiose [(GlcNAc)(2)] in Streptomyces coelicolor A3(2), although the gene encoding the ABC subunit that provides ATP hydrolysis for DasABC has not been identified. In this study, we disrupted the sequence that is highly homologous to the msiK gene, the product of which is an ABC subunit assisting several ABC permeases in other Streptomyces species. Disruption of msiK severely affected the ability of S. coelicolor A3(2) to utilize maltose, cellobiose, starch, cellulose, chitin and chitosan, but not glucose. The msiK null mutant lacked (GlcNAc)(2)-uptake activity, but GlcNAc transport activity was unaffected. The data indicated that msiK is essential for (GlcNAc)(2) uptake, which in S. coelicolor A3(2) is governed by ABC transporters including the DasABC-MsiK system, in contrast to Escherichia coli and Serratia marcescens, in which (GlcNAc)(2) uptake is mediated by the phosphotransferase system. Interestingly, the induction of chitinase production by (GlcNAc)(2) or chitin was absent in the msiK null mutant, unlike in the parent strain M145. The defect in chitinase gene induction was rescued by expressing the His-tagged MsiK protein under the control of the putative native promoter on a multicopy plasmid. The data suggest that uptake of (GlcNAc)(2) is necessary for induction of chitinase production. The msiK gene was constitutively transcribed, whereas the transcription of dasA [(GlcNAc)(2)-binding protein gene], malE (putative maltose-binding protein gene), cebE1 (putative cellobiose-binding protein gene) and bxlE1 (putative xylobiose-binding protein gene) was induced by their corresponding sugar ligands. This is believed to be the first report to indicate that (GlcNAc)(2) uptake mediated by ABC transporters is essential for chitinase production in streptomycetes, which are known to be the main degraders of chitin in soil.
dasABC基因编码一种ATP结合盒（ABC）转运蛋白，它是天蓝色链霉菌A3(2)中N,N'-二乙酰壳二糖[（GlcNAc）(2)]的摄取系统之一，尽管尚未鉴定出为DasABC提供ATP水解作用的ABC亚基的编码基因。在本研究中，我们破坏了与msiK基因高度同源的序列，该基因的产物是一种ABC亚基，可协助其他链霉菌属物种中的几种ABC通透酶发挥作用。msiK基因的破坏严重影响了天蓝色链霉菌A3(2)利用麦芽糖、纤维二糖、淀粉、纤维素、几丁质和壳聚糖的能力，但不影响其利用葡萄糖的能力。msiK基因缺失突变体缺乏（GlcNAc）(2)摄取活性，但GlcNAc转运活性不受影响。数据表明，msiK对于（GlcNAc）(2)的摄取至关重要，在天蓝色链霉菌A3(2)中，（GlcNAc）(2)的摄取由包括DasABC-MsiK系统在内的ABC转运蛋白控制，这与大肠杆菌和粘质沙雷氏菌不同，在大肠杆菌和粘质沙雷氏菌中，（GlcNAc）(2)的摄取由磷酸转移酶系统介导。有趣的是，与亲本菌株M145不同，msiK基因缺失突变体中不存在由（GlcNAc）(2)或几丁质诱导的几丁质酶产生。通过在多拷贝质粒上假定的天然启动子控制下表达His标签的MsiK蛋白，挽救了几丁质酶基因诱导的缺陷。数据表明，（GlcNAc）(2)的摄取是诱导几丁质酶产生所必需的。msiK基因组成型转录，而dasA[（GlcNAc）(2)结合蛋白基因]、malE（假定的麦芽糖结合蛋白基因）、cebE1（假定的纤维二糖结合蛋白基因）和bxlE1（假定的木二糖结合蛋白基因）的转录由它们相应的糖配体诱导。据信，这是第一份表明ABC转运蛋白介导的（GlcNAc）(2)摄取对于链霉菌中几丁质酶产生至关重要的报告，链霉菌是已知的土壤中几丁质的主要降解菌。
