TLXI, a novel type of xylanase inhibitor from wheat (Triticum aestivum) belonging to the thaumatin family
TLXI, a novel type of xylanase inhibitor from wheat (Triticum aestivum) belonging to the thaumatin family
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DOI：
10.1042/bj20061291
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发表时间：
2007-05-01
影响因子：
4.1
通讯作者：
Delcour, Jan A.
中科院分区：
文献类型：
--
作者：
Fierens, Ellen;Rombouts, Sigrid;Delcour, Jan A.
小麦（小麦）含有一种以前未知类型的木聚糖酶（EC 3.2.1.8）抑制剂，本文首次对其进行了描述。基于其与TLP（奇异果甜蛋白样蛋白）> 60%的相似性以及其含有Prosite PS 00316奇异果甜蛋白家族标签的事实，其被称为TLXI（奇异果甜蛋白样木聚糖酶抑制剂）。TLXI是一种碱性（等电点>= 9.3，等电聚焦）蛋白质，分子量约为1000。18 kDa（通过SDS/PAGE测定），并且其存在于小麦中，具有不同程度的糖基化。TLXI基因序列编码26个氨基酸的信号序列，随后是151个氨基酸的成熟蛋白，计算分子量为15.6 kDa，pI为8.38。在毕赤酵母中成功表达了TLXI成熟蛋白，经SDS/PAGE检测，重组蛋白的分子量约为21 kDa。从小麦中纯化的TLXI的多克隆抗体与rTLXI的表位以及与索马甜的表位反应，表明这三种蛋白质之间具有高度的结构相似性。TLXI具有独特的抑制特异性。它是许多糖苷水解酶家族11木聚糖酶的非竞争性抑制剂，但它对糖苷水解酶家族10木聚糖酶是无活性的。进展曲线显示TLXI是缓慢的紧密结合抑制剂，Ki约为0.001。60 nM。除了玉米蛋白（一种来自玉米（Zea mays）的α-淀粉酶/胰蛋白酶抑制剂）之外，目前在TLP中还没有其他已知的酶抑制剂。因此，TLXI代表了这组蛋白质中的一种新型抑制剂。
Wheat (Triticum aestivum) contains a previously unknown type of xylanase (EC 3.2.1.8) inhibitor, which is described in the present paper for the first time. Based on its > 60 % similarity to TLPs (thaumatin-like proteins) and the fact that it contains the Prosite PS00316 thaumatin family signature, it is referred to as TLXI (thaumatin-like xylanase inhibitor). TLXI is a basic (pI >=, 9.3 in isoelectric focusing) protein with a molecular mass of approx. 18 kDa (determined by SDS/PAGE) and it occurs in wheat with varying extents of glycosylation. The TLXI gene sequence encodes a 26-amino-acid signal sequence followed by a 151-amino-acid mature protein with a calculated molecular mass of 15.6 kDa and pl of 8.38. The mature TLXI protein was expressed successfully in Pichia pastoris, resulting in a 21 kDa (determined by SDS/PAGE) recombinant protein (rTLXI). Polyclonal antibodies raised against TLXI purified from wheat react with epitopes of rTLXI as well as with those of thaumatin, demonstrating high structural similarity between these three proteins. TLXI has a unique inhibition specificity. It is a noncompetitive inhibitor of a number of glycoside hydrolase family 11 xylanases, but it is inactive towards glycoside hydrolase family 10 xylanases, Progress curves show that TLXI is a slow tight-binding inhibitor, with a K-i of approx. 60 nM. Except for zeamatin, an alpha-amylase/trypsin inhibitor from maize (Zea mays), no other enzyme inhibitor is currently known among the TLPs. TLXI thus represents a novel type of inhibitor within this group of proteins.