Multifunctional xylooligosaccharide/cephalosporin C deacetylase revealed by the hexameric structure of the Bacillus subtilis enzyme at 1.9 Å resolution
Multifunctional xylooligosaccharide/cephalosporin C deacetylase revealed by the hexameric structure of the Bacillus subtilis enzyme at 1.9 Å resolution
复制标题
DOI：
10.1016/s0022-2836(03)00632-6
复制
发表时间：
2003-07-11
影响因子：
5.6
通讯作者：
Brannigan, JA
中科院分区：
文献类型：
--
作者：
Vincent, F;Charnock, SJ;Brannigan, JA
根据氨基酸序列的相似性，活性在碳水化合物配体上的酯酶和脱乙酰酶被分为14个家族。来自碳水化合物酯酶家族7(CE-7)的酶是不寻常的，因为它们对乙酰化低聚木糖和抗生素头孢菌素C都表现出活性。枯草杆菌168的多功能CE-7酯酶(以下简称CAH)的1.9埃结构显示出一个经典的α/β水解酶折叠，包裹在32个六角体内。这是六聚体α/β水解酶的第一个例子，进一步证明了这一特定折叠的多功能性，它被广泛地用于各种生物环境中。一条狭窄的入口隧道通向分子的中心，在那里，六个活性中心催化三元化合物指向隧道内部，从而与细胞质内容物隔离。通过类似于自我分隔的蛋白酶，隧道入口可能起到阻碍大底物进入多特异性活性中心的作用。这就解释了观察到这种酶在各种小的乙酰化分子上是活跃的。活性部位突变体与反应产物醋酸酯形成的复合体的结构揭示了推测的氧阴离子结合部位的细节，并表明底物主要通过与蛋白质疏水残基的非特异性接触而结合。参与催化的蛋白质残基通过与典型的α/β水解酶折叠中的蛋白质漂移相互作用而被束缚。这些漂移也调节了四级结构的维持，因此似乎只有在蛋白质多聚体的情况下才能实现催化能力。我们认为CE-7家族的乙酰木聚糖酯酶(EC 3.1.1.72)和头孢菌素C脱乙酰基酶(EC 3.1.1.41)是一类对多种小底物具有多功能脱乙酰基酶活性的蛋白质。(C)2003爱思唯尔科学有限公司。保留所有权利。
Esterases and deacetylases active on carbohydrate ligands have been classified into 14 families based upon amino acid sequence similarities. Enzymes from carbohydrate esterase family seven (CE-7) are unusual in that they display activity towards both acetylated xylooligosaccharides and the antibiotic, cephalosporin C. The 1.9 Angstrom structure of the multifunctional CE-7 esterase (hereinafter CAH) from Bacillus subtilis 168 reveals a classical alpha/beta hydrolase fold encased within a 32 hexamer. This is the first example of a hexameric alpha/beta hydrolase and is further evidence of the versatility of this particular fold, which is used in a wide variety of biological contexts. A narrow entrance tunnel leads to the centre of the molecule, where the six active-centre catalytic triads point towards the tunnel interior and thus are sequestered away from cytoplasmic contents. By analogy to self-compartmentalising proteases, the tunnel entrance may function to hinder access of large substrates to the poly-specific active centre. This would explain the observation that the enzyme is active on a variety of small, acetylated molecules. The structure of an active site mutant in complex with the reaction product, acetate, reveals details of the putative oxyanion binding site, and suggests that substrates bind predominantly through non-specific contacts with protein hydrophobic residues. Protein residues involved in catalysis are tethered by interactions with protein excursions from the canonical alpha/beta hydrolase fold. These excursions also mediate quaternary structure maintenance, so it would appear that catalytic competence is only achieved on protein multimerisation. We suggest that the acetyl xylan esterase (EC 3.1.1.72) and cephalosporin C deacetylase (EC 3.1.1.41) enzymes of the CE-7 family represent a single class of proteins with a multifunctional deacetylase activity against a range of small substrates. (C) 2003 Elsevier Science Ltd. All rights reserved.