Brass J M, Bauer K, Ehmann U, Boos W
J Bacteriol. 1985 Feb;161(2):720-6. doi: 10.1128/jb.161.2.720-726.1985.
Maltoporin (lambda receptor) is part of the maltose transport system in Escherichia coli and is necessary for the facilitated diffusion of maltose and maltodextrins across the outer membrane. Maltoporin also allows the diffusion of nonmaltodextrin substrates, albeit with less efficiency. The preference of maltoporin for maltodextrins in vivo is thought to be the result of an interaction of maltoporin with the maltose-binding protein, the malE gene product. In a recent report Heuzenroeder and Reeves (J. Bacteriol. 144:431-435, 1980) suggested that this interaction establishes a gating mechanism which inhibits the diffusion of nonmaltodextrin substrates, such as lactose. To reinvestigate this important conclusion, we constructed ompR malTc strains carrying either the malE+ gene, the nonpolar malE444 deletion, or the malE254 allele, which specifies an interaction-deficient maltose-binding protein. Lactose uptake was measured at different concentrations below the Km of this transport system and under conditions where transport was limited by the diffusion through maltoporin. We found no difference in the kinetics of lactose uptake irrespective of the malE allele. We conclude that the maltose-binding protein does not modulate the activity of maltoporin as a general outer membrane porin.
麦芽糖孔蛋白（λ受体）是大肠杆菌麦芽糖转运系统的一部分，对于麦芽糖和麦芽糊精跨外膜的易化扩散是必需的。麦芽糖孔蛋白也允许非麦芽糊精底物的扩散，尽管效率较低。麦芽糖孔蛋白在体内对麦芽糊精的偏好被认为是麦芽糖孔蛋白与麦芽糖结合蛋白（malE基因产物）相互作用的结果。在最近的一份报告中，Heuzenroeder和Reeves（《细菌学杂志》144:431 - 435，1980）提出这种相互作用建立了一种门控机制，该机制抑制非麦芽糊精底物（如乳糖）的扩散。为了重新研究这一重要结论，我们构建了携带malE +基因、非极性malE444缺失或malE254等位基因的ompR malTc菌株，其中malE254等位基因编码一种缺乏相互作用的麦芽糖结合蛋白。在低于该转运系统Km的不同浓度下以及在转运受通过麦芽糖孔蛋白的扩散限制的条件下测量乳糖摄取。我们发现无论malE等位基因如何，乳糖摄取动力学没有差异。我们得出结论，麦芽糖结合蛋白并不作为一般的外膜孔蛋白调节麦芽糖孔蛋白的活性。
