Maltose binding protein (MalE) interacts with periplasmic loops P2 and P1 respectively of the MalFG subunits of the maltose ATP binding cassette transporter (MalFGK2) from Escherichia coli Salmonella during the transport cycle
Maltose binding protein (MalE) interacts with periplasmic loops P2 and P1 respectively of the MalFG subunits of the maltose ATP binding cassette transporter (MalFGK2) from Escherichia coli Salmonella during the transport cycle
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DOI：
10.1111/j.1365-2958.2007.05982.x
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发表时间：
2007-12-01
影响因子：
3.6
通讯作者：
Schneider, Erwin
中科院分区：
文献类型：
--
作者：
Daus, Martin L.;Berendt, Susanne;Schneider, Erwin
在大肠杆菌/鼠伤寒沙门氏菌中，介导麦芽糖/麦芽糊精摄取的三磷酸腺苷结合盒(ABC-)转运体是最具特性的系统之一，是研究ABC进口体发挥作用的分子机制的模型。转运蛋白由一个周质麦芽糖结合蛋白(MAIE)和一个膜结合复合体(MAIFGK(2))组成，膜结合复合体包括形成孔的疏水亚基MAIF和MalG，以及ABC亚基MALK的两个拷贝。我们报告了在maIFG内分离到抑制突变，该突变部分恢复了携带maIK809等位基因(MaIKQ140K)的麦芽糖阴性突变体的运输。该突变影响与ATP结合有关的保守的LSGGQ基序。4个抑制子突变中有3个分别位于MAIFG的周质环P2和P1。交叉连接数据显示，这些区域与Maie很接近。特别是，体内外研究表明，无底物和有底物的MAIE的Gly-13与MAIG的Pro-78密切接触。这些数据表明，Male通过其N-末端结构域与MAIG-P1永久地密切接触。总之，我们的结果被解释为支持底物可用性通过MAIFG的胞外环从MAIE传递到MAIK二聚体的概念，并结合当前的运输模型进行了讨论。
The ATP binding cassette (ABC-) transporter mediating the uptake of maltose/maltodextrins in Escherichia coli/Salmonella enterica serovar Typhimurium is one of the best characterized systems and serves as a model for studying the molecular mechanism by which ABC importers exert their functions. The transporter is composed of a periplasmic maltose binding protein (MaIE), and a membrane-bound complex (MaIFGK(2)), comprising the pore-forming hydrophobic subunits, MaIF and MalG, and two copies of the ABC subunit, MalK. We report on the isolation of suppressor mutations within maIFG that partially restore transport of a maltose-negative mutant carrying the maIK809 allele (MaIKQ140K). The mutation affects the conserved LSGGQ motif that is involved in ATP binding. Three out of four suppressor mutations map in periplasmic loops P2 and P1 respectively of MaIFG. Cross-linking data revealed proximity of these regions to MaIE. In particular, as demonstrated in vitro and in vivo, Gly-13 of substrate-free and substrate-loaded MaIE is in close contact to Pro-78 of MaIG. These data suggest that MalE is permanently in close contact to MaIG-P1 via its N-terminal domain. Together, our results are interpreted in favour of the notion that substrate availability is communicated from MaIE to the MaIK dimer via extracytoplasmic loops of MaIFG, and are discussed with respect to a current transport model.