Bukowska Magdalena A, Hohl Michael, Geertsma Eric R, Hürlimann Lea M, Grütter Markus G, Seeger Markus A
†Department of Biochemistry, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland.
‡Institute of Medical Microbiology, University of Zurich, Gloriastrasse 30/32, 8006 Zurich, Switzerland.
Biochemistry. 2015 May 19;54(19):3086-99. doi: 10.1021/acs.biochem.5b00188. Epub 2015 May 7.
ABC exporters are ubiquitous multidomain transport proteins that couple ATP hydrolysis at a pair of nucleotide binding domains to substrate transport across the lipid bilayer mediated by two transmembrane domains. Recently, the crystal structure of the heterodimeric ABC exporter TM287/288 was determined. One of its asymmetric ATP binding sites is called the degenerate site; it binds nucleotides tightly but is impaired in terms of ATP hydrolysis. Here we report the crystal structures of both isolated motor domains of TM287/288. Unexpectedly, structural elements constituting the degenerate ATP binding site are disordered in these crystals and become structured only in the context of the full-length transporter. In addition, hydrogen bonding patterns of key residues, including those of the catalytically important Walker B and the switch loop motifs, are fundamentally different in the solitary NBDs compared to those in the intact transport protein. The structures reveal crucial interdomain contacts that need to be established for the proper assembly of the functional transporter complex.
ABC转运蛋白是普遍存在的多结构域转运蛋白，它将一对核苷酸结合结构域处的ATP水解与由两个跨膜结构域介导的跨脂质双层的底物转运偶联起来。最近，异源二聚体ABC转运蛋白TM287/288的晶体结构得以确定。其一个不对称ATP结合位点被称为简并位点；它能紧密结合核苷酸，但在ATP水解方面存在缺陷。在此，我们报道了TM287/288两个分离的马达结构域的晶体结构。出乎意料的是，构成简并ATP结合位点的结构元件在这些晶体中是无序的，仅在全长转运蛋白的背景下才形成结构。此外，与完整转运蛋白中的情况相比，包括催化重要的沃克B基序和开关环基序在内的关键残基的氢键模式在单独的核苷酸结合结构域中存在根本差异。这些结构揭示了功能性转运蛋白复合物正确组装所需建立的关键结构域间接触。
