Nikaido K, Ames G F
Department of Molecular and Cell Biology, Division of Biochemistry and Molecular Biology, University of California, Berkeley, California 94720-3202, USA.
J Biol Chem. 1999 Sep 17;274(38):26727-35. doi: 10.1074/jbc.274.38.26727.
The membrane-bound complex of the Salmonella typhimurium histidine permease, a member of the ABC transporters (or traffic ATPases) superfamily, is composed of two integral membrane proteins, HisQ and HisM, and two copies of an ATP-binding subunit, HisP, which hydrolyze ATP, thus supplying the energy for translocation. The three-dimensional structure of HisP has been resolved. Extensive evidence indicates that the HisP subunits form a dimer. We investigated the mechanism of action of such a dimer, both within the complex and in soluble form, by creating heterodimers between the wild type and mutant HisP proteins. The data strongly suggest that within the complex both subunits hydrolyze ATP and that one subunit is activated by the other. In a heterodimer containing one wild type and one hydrolysis defective subunit both hydrolysis and ligand translocation occur at half the rate of the wild type. Soluble HisP also hydrolyzes ATP if one subunit is inactive; its specific activity is identical to that of the wild type, indicating that only one of the subunits in a soluble dimer is involved in hydrolysis. We show that the activating ability varies depending on the nature of the substitution of a well conserved residue, His-211.
鼠伤寒沙门氏菌组氨酸通透酶是ABC转运蛋白（或运输ATP酶）超家族的成员，其膜结合复合物由两个整合膜蛋白HisQ和HisM以及两个ATP结合亚基HisP组成，HisP水解ATP，从而为转运提供能量。HisP的三维结构已得到解析。大量证据表明HisP亚基形成二聚体。我们通过在野生型和突变型HisP蛋白之间创建异源二聚体，研究了这种二聚体在复合物内部以及可溶性形式下的作用机制。数据强烈表明，在复合物中两个亚基都能水解ATP，且一个亚基被另一个亚基激活。在含有一个野生型亚基和一个水解缺陷亚基的异源二聚体中，水解和配体转运的速率均为野生型的一半。如果一个亚基无活性，可溶性HisP也能水解ATP；其比活性与野生型相同，表明可溶性二聚体中只有一个亚基参与水解。我们发现，激活能力会因保守残基His-211的取代性质不同而有所变化。
