Crystal structures of soybean beta-amylase reacted with beta-maltose and maltal: active site components and their apparent roles in catalysis.
Crystal structures of soybean beta-amylase reacted with beta-maltose and maltal: active site components and their apparent roles in catalysis.
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DOI：
10.2210/pdb1bya/pdb
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发表时间：
1994-06
期刊：
影响因子：
2.9
通讯作者：
B. Mikami;M. Degano;E. Hehre;J. Sacchettini
中科院分区：
文献类型：
--
作者：
B. Mikami;M. Degano;E. Hehre;J. Sacchettini
在1.9-2.2-A分辨率下测定了无配体和用小底物（β-麦芽糖、麦芽醛）浸泡的具有催化活性的大豆β-淀粉酶的晶体结构。两个β-麦芽糖底物分子串联结合到蛋白质上，其中一些麦芽四糖酶促缩合产物共享相同的结合位点。用麦芽醛浸泡的β-淀粉酶显示出2-脱氧麦芽糖（酶的水合产物）的两个结合分子的类似排列。在每种情况下，糖配体的非还原末端朝向蛋白质活性位点口袋的基部。催化中心位于结合的二糖之间，并且在口袋中发现比抑制剂α-环糊精结合的地方更深，其特征在于存在两个保守的谷氨酸残基的相反布置的羧基。Glu 186的OE 2羧基低于结合麦芽四糖的倒数第二个葡萄糖残基（Glc 2）的平面，距离该配体的倒数第二个α-1，4-糖苷键的氧原子2.6 A。Glu 380的OE 2羧基位于Glc 2平面上方，距离更深结合的β-麦芽糖的O-1原子2.8 A。阿糖胞苷结合不改变这两个羧基的空间坐标或57-kDa蛋白质的整体构象。然而，活性酶的糖复合物与邻接活性位点口袋的环（L3）的肽段中的显著（10 A）局部构象变化相关。（250字处删节）
The crystal structures of catalytically competent soybean beta-amylase, unliganded and bathed with small substrates (beta-maltose, maltal), were determined at 1.9-2.2-A resolution. Two molecules of beta-maltose substrate bind to the protein in tandem, with some maltotetraose enzymic condensation product sharing the same binding sites. The beta-amylase soaked with maltal shows a similar arrangement of two bound molecules of 2-deoxymaltose, the enzymic hydration product. In each case the nonreducing ends of the saccharide ligands are oriented toward the base of the protein's active site pocket. The catalytic center, located between the bound disaccharides and found deeper in the pocket than where the inhibitor alpha-cyclodextrin binds, is characterized by the presence of oppositely disposed carboxyl groups of two conserved glutamic acid residues. The OE2 carboxyl of Glu 186 is below the plane of the penultimate glucose residue (Glc 2) of bound maltotetraose, 2.6 A from the oxygen atom of that ligand's penultimate alpha-1,4-glucosidic linkage. The OE2 carboxyl of Glu 380 lies above the plane of Glc 2, 2.8 A from the O-1 atom of the more deeply bound beta-maltose. Saccharide binding does not alter the spatial coordinates of these two carboxyl groups or the overall conformation of the 57-kDa protein. However, the saccharide complexes of the active enzyme are associated with a significant (10 A) local conformational change in a peptide segment of a loop (L3) that borders the active site pocket.(ABSTRACT TRUNCATED AT 250 WORDS)