Nucleotide sequences of two contiguous and highly homologous xylanase genes xynA and xynB and characterization of XynA from Clostridium thermocellum
Nucleotide sequences of two contiguous and highly homologous xylanase genes xynA and xynB and characterization of XynA from Clostridium thermocellum
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DOI：
10.1007/s002530051401
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发表时间：
1999-03-01
影响因子：
5
通讯作者：
Ohmiya, K
中科院分区：
文献类型：
--
作者：
Hayashi, H;Takehara, M;Ohmiya, K
一个5.7 kbp的热纤梭菌F1 DNA的区域进行测序，发现含有两个连续的和高度同源的木聚糖酶基因，xynA和xynB。编码木聚糖酶XynA的xynA基因由2049 bp组成，编码683个氨基酸的蛋白质，分子量为74 511 Da，编码木聚糖酶XynB的xynB基因全长1371 bp，编码457个氨基酸，分子量为49883 Da。末端信号肽和以下顺序的四个结构域：家族11木聚糖酶结构域、家族VI纤维素结合结构域、锚定蛋白结构域和NodB结构域。XynB表现出与XynA极高的整体序列同源性（同一性96.9%），而缺乏后者中存在的NodB结构域。这些事实表明，xynA和xynB基因起源于一个共同的祖先基因通过基因复制。从重组大肠杆菌菌株中纯化了XynA并进行了表征。纯化的酶是高度活跃的：朝木聚糖;燕麦斯佩耳特木聚糖的比活性为689单位/毫克蛋白质。免疫学和酶谱分析表明，XynA和XynB是C. Thermocellum F1纤维素酶体。
A 5.7-kbp region of the Clostridium thermocellum F1 DNA was sequenced and found to contain two contiguous and highly homologous xylanase genes, xynA and xynB. The xynA gene encoding the xylanase XynA consists of 2049 bp and encodes a protein of 683 amino acids with a molecular mass of 74 511 Da, and the xynB gene encoding the xylanase XynB consists of 1371 bp and encodes a protein of 457 amino acids with a molecular mass of 49 883 Da. XynA is a modular enzyme composed of a typical N-terminal signal peptide and four domains in the following order: a family-11 xylanase domain, a family-VI cellulose-binding domain, a dockerin domain, and a NodB domain. XynB exhibited extremely high overall sequence homology with XynA (identity 96.9%), while lacking the NodB domain present in the latter. These facts suggested that the xynA and xynB genes originated from a common ancestral gene through gene duplication. XynA was purified from a recombinant Escherichia coli strain and characterized. The purified enzyme was highly active: toward xylan; the specific activity on oat-spelt xylan was 689 units/ mg protein. Immunological and zymogram analyses suggested that XynA and XynB are components of the C. thermocellum F1 cellulosome.