Zhang Y, Conway C, Rosato M, Suh Y, Manson M D
Department of Biology, Texas A & M University, College Station 77843-3258.
J Biol Chem. 1992 Nov 15;267(32):22813-20.
The periplasmic maltose-binding protein (MBP) of Escherichia coli is the recognition component of the maltose chemoreceptor and of the active transport system for maltose. It interacts with the Tar chemotactic signal transducer and the integral cytoplasmic-membrane components (the MalF and MalG proteins) of the maltose transport system. Maltose binds in a cleft between the globular N-terminal and C-terminal domains of MBP, which are connected by a moveable hinge. The two domains undergo a large motion relative to one another as the protein moves from the open, unbound state to the closed, ligand-bound state. We generated, by doped-primer mutagenesis, amino acid substitutions that specifically disrupt the chemotactic function of MBP. These substitutions cluster in two well-defined regions that are nearly contiguous on the surface of MBP in its closed conformation. One region is in the N-terminal domain and one is in the C-terminal domain. The distance between the two regions is expected to change substantially as the protein goes from the open to the closed form. These results support a model in which ligand binding brings two recognition sites on MBP into the proper spatial relationship to interact with complementary sites on Tar. Mutations in MBP that appear to cause defects in interaction with MalF and MalG are distributed differently from mutations that primarily affect maltose taxis. We conclude that the regions of MBP that contact Tar and those that contact MalF and MalG are adjacent on the face of the protein opposite the hinge connecting the two domains and that those regions are largely, although perhaps not entirely, distinct.
大肠杆菌的周质麦芽糖结合蛋白（MBP）是麦芽糖化学感受器和麦芽糖主动运输系统的识别成分。它与Tar趋化信号转导器以及麦芽糖运输系统的整合细胞质膜成分（MalF和MalG蛋白）相互作用。麦芽糖结合在MBP球状N端和C端结构域之间的裂隙中，这两个结构域通过一个可移动的铰链相连。当蛋白质从开放的未结合状态转变为封闭的配体结合状态时，这两个结构域会相对彼此发生大幅度移动。我们通过掺杂引物诱变产生了特异性破坏MBP趋化功能的氨基酸取代。这些取代集中在两个明确界定的区域，在MBP封闭构象的表面上几乎相邻。一个区域在N端结构域，另一个区域在C端结构域。随着蛋白质从开放形式转变为封闭形式，这两个区域之间的距离预计会发生显著变化。这些结果支持了一种模型，即配体结合使MBP上的两个识别位点形成适当的空间关系，以便与Tar上的互补位点相互作用。MBP中似乎导致与MalF和MalG相互作用缺陷的突变分布与主要影响麦芽糖趋化性的突变不同。我们得出结论，MBP上与Tar接触的区域以及与MalF和MalG接触的区域在蛋白质表面与连接两个结构域的铰链相对的一侧相邻，并且这些区域在很大程度上（尽管可能不完全）是不同的。
