A 3D structure model of the melibiose permease of Escherichia coli represents a distinctive fold for Na+ symporters.
A 3D structure model of the melibiose permease of Escherichia coli represents a distinctive fold for Na+ symporters.
复制标题
大肠杆菌蜜二糖通透酶的 3D 结构模型代表了 Na 同向转运蛋白的独特折叠。
DOI：
10.1073/pnas.0905516106
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发表时间：
2009
影响因子：
11.1
通讯作者：
Guan,Lan
中科院分区：
文献类型：
--
作者：
Yousef,MohammadS;Guan,Lan
大肠杆菌蜜二糖通透酶（MelB）催化半乳糖苷与阳离子（Na+、Li+或H+）的偶联化学计量同向转运，使用来自一种共底物的向下易位的自由能来催化另一种共底物的积累。在这里，我们提出了一个3D结构模型的MelB线程通过晶体结构的乳糖通透酶的E。大肠杆菌（LacY），手动调整，并大力最小化。该模型包含442个连续残基（约94%的多肽），包括所有12个跨膜螺旋和连接环，没有空间冲突，并与模板结构很好地重叠。从模型计算的静电表面电位是典型的膜蛋白，并表现出一个特征环的细胞质侧周围的正电荷。3D模型表明MelB由两个假对称的6-螺旋束组成，内衬内部亲水腔，其面向膜的细胞质侧。糖和阳离子结合位点都被认为位于内部空腔内。该模型与许多以前的突变，生化/生物物理表征以及低分辨率结构数据是一致的。因此，讨论了具有顺序绑定的交替访问机制。建议的整体折叠MelB是从其他Na+耦合转运蛋白的可用晶体结构不同，这表明一个独特的折叠Na+同向转运蛋白。
The melibiose permease of Escherichia coli (MelB) catalyzes the coupled stoichiometric symport of a galactoside with a cation (either Na+, Li+, or H+), using free energy from the downhill translocation of one cosubstrate to catalyze the accumulation of the other. Here, we present a 3D structure model of MelB threaded through a crystal structure of the lactose permease of E. coli (LacY), manually adjusted, and energetically minimized. The model contains 442 consecutive residues (≈94% of the polypeptide), including all 12 transmembrane helices and connecting loops, with no steric clashes and superimposes well with the template structure. The electrostatic surface potential calculated from the model is typical for a membrane protein and exhibits a characteristic ring of positive charges around the periphery of the cytoplasmic side. The 3D model indicates that MelB consists of two pseudosymmetrical 6-helix bundles lining an internal hydrophilic cavity, which faces the cytoplasmic side of the membrane. Both sugar and cation binding sites are proposed to lie within the internal cavity. The model is consistent with numerous previous mutational, biochemical/biophysical characterizations as well as low-resolution structural data. Thus, an alternating access mechanism with sequential binding is discussed. The proposed overall fold of MelB is different from the available crystal structures of other Na+-coupled transporters, suggesting a distinctive fold for Na+symporters.