A novel family 8 xylanase, functional and physicochemical characterization
A novel family 8 xylanase, functional and physicochemical characterization
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DOI：
10.1074/jbc.m204517200
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发表时间：
2002-09-20
影响因子：
4.8
通讯作者：
Gerday, C
中科院分区：
文献类型：
--
作者：
Collins, T;Meuwis, MA;Gerday, C
木聚糖酶一般分为糖基水解酶家族10和11，它们的等电点与分子质量之间经常存在着相反的关系。然而，我们已经分离到一种嗜冷性木聚糖酶，它属于家族8，具有高等电点和高分子质量。这种新的木聚糖酶是从南极浮游假交替单胞菌中分离出来的，与第10或11家族的酶没有同源性，但与第8家族的成员有20%-30%的同源性。NAIR分析表明，与其他已知的保留木聚糖酶相反，该酶以反常构型进行水解。未检测到纤维素酶、壳聚糖酶和地衣质酶活性。它似乎在功能上类似于木聚糖酶家族11。它主要将木聚糖水解成木三糖和木四糖，在长链低聚木糖中活性最高。动力学研究表明，它有一个大的底物结合裂解，包含至少六个木糖结合亚基。观察到了低温下高催化活性和低热稳定性的典型嗜冷性特征。8个酶家族的进化树揭示了6个不同的簇的存在。实际上，将木聚糖酶归类到家族8会显示(α/α)(6)折叠，这与目前已知的其他木聚糖酶不同。
Xylanases are generally classified into glycosyl hydrolase families 10 and 11 and are found to frequently have an inverse relationship between their pI and molecular mass values. However, we have isolated a psychrophilic xylanase that belongs to family 8 and which has both a high pI and high molecular mass. This novel xylanase, isolated from the Antarctic bacterium Pseudoalteromonas haloplanktis, is not homologous to family 10 or 11 enzymes but has 20-30% identity with family 8 members. NAIR analysis shows that this enzyme hydrolyzes with inversion of anomeric configuration, in contrast to other known xylanases which are retaining. No cellulase, chitosanase or lichenase activity was detected. It appears to be functionally similar to family 11 xylanases. It hydrolyzes xylan to principally xylotriose and xylotetraose and is most active on long chain xylo-oligosaccharides. Kinetic studies indicate that it has a large substrate binding cleft, containing at least six xylose-binding subsites. Typical psychrophilic characteristics of a high catalytic activity at low temperatures and low thermal stability are observed. An evolutionary tree of family 8 enzymes revealed the presence of six distinct clusters. Indeed classification in family 8 would suggest an (alpha/alpha)(6) fold, distinct from that of other currently known xylanases.