The X-ray crystallographic structure of Escherichia coli branching enzyme
The X-ray crystallographic structure of Escherichia coli branching enzyme
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DOI：
10.1074/jbc.m205746200
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发表时间：
2002-11-01
影响因子：
4.8
通讯作者：
Geiger, JH
中科院分区：
文献类型：
--
作者：
Abad, MC;Binderup, K;Geiger, JH
分支酶催化糖原或淀粉中α-1，6分支点的形成。我们报道了大肠杆菌糖原分支酶的2.3埃晶体结构。该酶由三个主要结构域组成，NH 2-末端七链β-夹心结构域，COOH-末端结构域和含有酶活性位点的中央α/β-桶结构域。虽然中心结构域与所有其他淀粉酶家族的酶相似，但分支酶仅与异淀粉酶共享所有三个结构域的结构。寡糖结合被建模或使用各种α-淀粉酶和环糊精葡聚糖转移酶的酶-寡糖复合物结构的分支酶，并且残基涉及寡糖结合。虽然大多数寡糖在分支酶结构中建模良好，但需要两个葡萄糖单元之间的约50度旋转以避免与分支酶的Trp（298）的空间冲突。在哺乳动物α-淀粉酶结构中观察到由该结构中的等效色氨酸残基引起的类似旋转。在这些结构中，寡糖似乎有两种结合模式，这取决于该芳香残基的身份和位置。
Branching enzyme catalyzes the formation of alpha-1,6 branch points in either glycogen or starch. We report the 2.3-Angstrom crystal structure of glycogen branching enzyme from Escherichia coli. The enzyme consists of three major domains, an NH2-terminal seven-stranded beta-sandwich domain, a COOH-terminal domain, and a central alpha/beta-barrel domain containing the enzyme active site. While the central domain is similar to that of all the other amylase family enzymes, branching enzyme shares the structure of all three domains only with isoamylase. Oligosaccharide binding was modeled or branching enzyme using the enzyme-oligosaccharide complex structures of various alpha-amylases and cyclodextrin glucanotransferase and residues were implicated in oligosaccharide binding. While most of the oligosaccharides modeled well in the branching enzyme structure, an approximate 50degrees rotation between two of the glucose units was required to avoid steric clashes with Trp(298) of branching enzyme. A similar rotation was observed in the mammalian alpha-amylase structure caused by an equivalent tryptophan residue in this structure. It appears that there are two binding modes for oligosaccharides in these structures depending on the identity and location of this aromatic residue.