MECHANISM OF MALTOSE TRANSPORT IN ESCHERICHIA-COLI - TRANSMEMBRANE SIGNALING BY PERIPLASMIC BINDING-PROTEINS
MECHANISM OF MALTOSE TRANSPORT IN ESCHERICHIA-COLI - TRANSMEMBRANE SIGNALING BY PERIPLASMIC BINDING-PROTEINS
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DOI：
10.1073/pnas.89.6.2360
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发表时间：
1992-03-15
影响因子：
11.1
通讯作者：
NIKAIDO, H
中科院分区：
文献类型：
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作者：
DAVIDSON, AL;SHUMAN, HA;NIKAIDO, H
麦芽糖通过大肠杆菌细胞质膜的转运依赖于周质麦芽糖结合蛋白（MBP）的存在，MBP是malE基因的产物。malF、malG和malK基因的产物形成膜相关复合物，其催化ATP水解以提供用于运输事件的能量。以前，分离的突变体已经获得了在没有MBP的情况下在麦芽糖上生长的能力。重组后的运输复合物进入蛋白脂质体，测量的ATP酶活性的野生型和突变体复合物的存在和不存在的MBP显示，野生型复合物水解ATP迅速只有当MBP和麦芽糖都存在。相反，突变体复合物在不存在麦芽糖和MBP的情况下获得了水解ATP的能力。不同突变体复合物的基础水解速率与该菌株对麦芽糖的生长速率成正比，结果表明组成性ATP水解以及推测复合物由此产生的环状构象变化在不存在MBP的情况下产生麦芽糖转运。这些结果还表明，ATP水解是不直接耦合到配体运输，即使在野生型细胞和MBP的一个重要功能是跨膜信号，通过跨膜MalF和MalG蛋白，在膜的另一侧的MalK蛋白，使ATP水解可以发生。
Maltose transport across the cytoplasmic membrane of Escherichia coli is dependent on the presence of a periplasmic maltose-binding protein (MBP), the product of the malE gene. The products of the malF, malG, and malK genes form a membrane-associated complex that catalyzes the hydrolysis of ATP to provide energy for the transport event. Previously, mutants were isolated that had gained the ability to grow on maltose in the absence of MBP. After reconstitution of the transport complex into proteoliposomes, measurement of the ATPase activity of wild-type and mutant complexes in the presence and absence of MBP revealed that the wild-type complex hydrolyzed ATP rapidly only when MBP and maltose were both present. In contrast, the mutant complexes have gained the ability to hydrolyze ATP in the absence of maltose and MBP. The basal rate of hydrolysis by the different mutant complexes was directly proportional to the growth rate of that strain on maltose, a result indicating that the constitutive ATP hydrolysis and presumably the resultant cyclic conformational changes of the complex produce maltose transport in the absence of MBP. These results also suggest that ATP hydrolysis is not directly coupled to ligand transport even in wild-type cells and that one important function of MBP is to transmit a transmembrane signal, through the membrane-spanning MalF and MalG proteins, to the MalK protein on the other side of the membrane, so that ATP hydrolysis can occur.