Translocation mechanism of long sugar chains across the maltoporin membrane channel
Translocation mechanism of long sugar chains across the maltoporin membrane channel
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DOI：
10.1016/s0969-2126(02)00811-0
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发表时间：
2002-09-01
期刊：
影响因子：
5.7
通讯作者：
Fischer, S
中科院分区：
文献类型：
--
作者：
Dutzler, R;Schirmer, T;Fischer, S
麦芽糊精允许麦芽糊精长链的渗透。它与两亲性糖紧密结合，既与芳香族残基的螺旋线发生疏水作用，又与离子侧链形成氢键。麦芽六糖转位的最小能量路径是通过共轭峰精化方法得到的，该方法不加约束地优化连续的构象串。这表明蛋白质是被动的，而糖则沿着芳香的小巷螺旋式滑动。糖羟基H键配对的近乎瞬间的转换导致了两个小的能量势垒(每个势垒都类似于4千卡/摩尔)，在寄存器移位一个葡萄糖单位的过程中，这与对不同糖链长度的实验解离速率的动力学分析是一致的。因此，麦芽糖蛋白的功能就像一种有效的易位“酶”，而寄存器移位的缓慢速度(类似于1/ms)是由于高碰撞摩擦造成的。
Maltoporin allows permeation of long maltodextrin chains. It tightly binds the amphiphilic sugar, offering both hydrophobic interactions with a helical lane of aromatic residues and H bonds with ionic side chains. The minimum-energy path of maltohexaose translocation is obtained by the conjugate peak refinement method, which optimizes a continuous string of conformers without applying constraints. This reveals that the protein is passive while the sugar glides screw-like along the aromatic lane. Near instant switching of sugar hydroxyl H bond partners results in two small energy barriers (of similar to4 kcal/mol each) during register shift by one glucosyl unit, in agreement with a kinetic analysis of experimental dissociation rates for varying sugar chain lengths. Thus, maltoporin functions like an efficient translocation "enzyme," and the slow rate of the register shift (similar to1/ms) is due to high collisional friction.