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首页> 外文期刊>The FEBS journal >Crystal structure determination and inhibition studies of a novel xylanase and l-amylase inhibitor protein (XAIP) from Scadoxus multiflorus
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Crystal structure determination and inhibition studies of a novel xylanase and l-amylase inhibitor protein (XAIP) from Scadoxus multiflorus

机译：何首乌的木聚糖酶和l-淀粉酶抑制剂蛋白（XAIP）的晶体结构测定和抑制研究

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摘要

A novel plant protein isolated from the underground bulbs of Scadoxus multiflorus, xylanase and l-amylase inhibitor protein (XAIP), inhibits two structurally and functionally unrelated enzymes: xylanase and l-amylase. The mature protein contains 272 amino acid residues which show sequence identities of 48% to the plant chitinase hevamine and 36% to xylanase inhibitor protein-I, a double-headed inhibitor of GH10 and GH11 xylanases. However, unlike hevamine, it is enzymatically inactive and, unlike xylanase inhibitor protein-I, it inhibits two functionally different classes of enzyme. The crystal structure of XAIP has been determined at 2.0 c resolution and refined to Rcryst and Rfree factors of 15.2% and 18.6%, respectively. The polypeptide chain of XAIP adopts a modified triosephosphate isomerase barrel fold with eight o-strands in the inner circle and nine l-helices forming the outer ring. The structure contains three cis peptide bonds: Gly33-Phe34, Tyr159-Pro160 and Trp253-Asp254. Although hevamine has a long accessible carbohydrate-binding channel, in XAIP this channel is almost completely filled with the side-chains of residues Phe13, Pro77, Lys78 and Trp253. Solution studies indicate that XAIP inhibits GH11 family xylanases and GH13 family l-amylases through two independent binding sites located on opposite surfaces of the protein. Comparison of the structure of XAIP with that of xylanase inhibitor protein-I, and docking studies, suggest that loops l3-o4 and l4-o5 may be involved in the binding of GH11 xylanase, and that helix l7 and loop o6-l6 are suitable for the interaction with l-amylase.
机译：从何首乌的地下鳞茎中分离出的一种新型植物蛋白，木聚糖酶和l-淀粉酶抑制剂蛋白（XAIP）抑制两种在结构和功能上不相关的酶：木聚糖酶和l-淀粉酶。成熟的蛋白质包含272个氨基酸残基，与植物几丁质酶七胺的序列同一性为48％，与木聚糖酶抑制剂蛋白I（GH10和GH11木聚糖酶的双头抑制剂）的序列同一性为36％。然而，与六胺不同，它在酶学上是无活性的，并且与木聚糖酶抑制剂蛋白-I不同，它抑制两种功能不同的酶。 XAIP的晶体结构已在2.0 c分辨率下测定，并分别精炼为15.2％和18.6％的Rcryst和Rfree因子。 XAIP的多肽链采用修饰的磷酸三糖异构酶桶状折叠，内圈有8条O链，外圈有9个L螺旋。该结构包含三个顺式肽键：Gly33-Phe34，Tyr159-Pro160和Trp253-Asp254。尽管七胺具有长的可与碳水化合物结合的通道，但在XAIP中，该通道几乎完全充满了残基Phe13，Pro77，Lys78和Trp253的侧链。溶液研究表明，XAIP通过位于蛋白质相对表面的两个独立结合位点抑制GH11家族木聚糖酶和GH13家族1-淀粉酶。 XAIP与木聚糖酶抑制剂蛋白I的结构比较以及对接研究表明，环1-34-1和1-4-5可能参与GH11木聚糖酶的结合，而螺旋17和1-6螺旋是合适的。与l-淀粉酶的相互作用。

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