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首页> 外文期刊>Biochimica et biophysica acta: BBA: International journal of biochemistry, biophysics and molecular biololgy. Proteins and Proteomics >Secretion of active xylanase C from Streptomyces lividans is exclusively mediated by the Tat protein export system
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Secretion of active xylanase C from Streptomyces lividans is exclusively mediated by the Tat protein export system

机译：链霉菌链霉菌中活性木聚糖酶C的分泌完全由Tat蛋白输出系统介导

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摘要

The bacterial twin-arginine translocation (Tat) pathway transports folded proteins across the cytoplasmic membrane. The precursors targeted to the Tat pathway have signal peptides bearing the consensus motif (S/T-R-R-X-F-L-K). The xylanase C (XlnC) of Streptomyces lividans is a 20-kDa secreted enzyme. The XlnC signal peptide is 49 amino acids long and contains the S-R-R-G-F-L-G sequence, which is similar to the twin-arginine consensus motif. In S. lividans, XlnC secretion was impaired in a tatC insertion mutant, which is unable to secrete proteins that are dependent on the Tat system. When the signal peptide of XlnC was replaced by the Sec-dependent signal peptide of xylanase A, XlnC was secreted as an inactive form and demonstrated rapid proteolytic degradation in the culture supernatant, thus indicating that XlnC was specifically secreted through the Tat system. Deletions of the n-region of the XlnC signal sequence showed that a minimum of six amino acids residues preceding the twin-arginine motif was required to secrete XlnC. Replacement of one or both arginines by lysine residues in the twin arginine motif decreased four- and sevenfold, respectively, the enzyme production but did not abolish it. However, pulse chase experiments showed that the half-life of the precursor was from 2 to 3 h instead of 11 min for the wild- type precursor. Since XlnC is not associated with cofactors to exhibit activity, it is therefore a newly identified prokaryotic non-redox Tat substrate.
机译：细菌双精氨酸易位（Tat）途径将折叠的蛋白质转运穿过细胞质膜。靶向Tat途径的前体具有带有共有基序的信号肽（S / T-R-R-X-F-L-K）。猪链霉菌的木聚糖酶C（XlnC）是一种20 kDa的分泌酶。 XlnC信号肽长49个氨基酸，并包含S-R-R-G-F-L-G序列，该序列与双精氨酸共有基序相似。在紫葡萄链球菌中，tatC插入突变体削弱了XlnC的分泌，该突变体无法分泌依赖于Tat系统的蛋白质。当XlnC的信号肽被木聚糖酶A的Sec依赖性信号肽替代时，XlnC以无活性形式分泌，并在培养上清液中显示出快速的蛋白水解降解，因此表明XlnC是通过Tat系统特异性分泌的。 XlnC信号序列的n-区的缺失表明，在双精氨酸基序之前至少需要六个氨基酸残基才能分泌XlnC。用双精氨酸基序中的赖氨酸残基替代一个或两个精氨酸，酶的产量分别降低了四倍和七倍，但并未消除。但是，脉冲追踪实验显示，前体的半衰期为2至3小时，而野生型前体的半衰期为11分钟。由于XlnC与显示活性的辅因子不相关，因此它是新近鉴定的原核非氧化还原Tat底物。

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