Exploring conformational equilibria of a heterodimeric ABC transporter

Elife. 2017 Jan 4;6:e20236. doi: 10.7554/eLife.20236.

Abstract

ABC exporters pump substrates across the membrane by coupling ATP-driven movements of nucleotide binding domains (NBDs) to the transmembrane domains (TMDs), which switch between inward- and outward-facing (IF, OF) orientations. DEER measurements on the heterodimeric ABC exporter TM287/288 from Thermotoga maritima, which contains a non-canonical ATP binding site, revealed that in the presence of nucleotides the transporter exists in an IF/OF equilibrium. While ATP binding was sufficient to partially populate the OF state, nucleotide trapping in the pre- or post-hydrolytic state was required for a pronounced conformational shift. At physiologically high temperatures and in the absence of nucleotides, the NBDs disengage asymmetrically while the conformation of the TMDs remains unchanged. Nucleotide binding at the degenerate ATP site prevents complete NBD separation, a molecular feature differentiating heterodimeric from homodimeric ABC exporters. Our data suggest hydrolysis-independent closure of the NBD dimer, which is further stabilized as the consensus site nucleotide is committed to hydrolysis.

Keywords: ABC transporter; DEER; E. coli; biophysics; electron paramagnetic resonance; structural biology.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • ATP-Binding Cassette Transporters / chemistry*
  • ATP-Binding Cassette Transporters / metabolism*
  • Adenosine Triphosphate / metabolism*
  • Models, Molecular
  • Protein Binding
  • Protein Conformation
  • Thermotoga maritima / enzymology*

Substances

  • ATP-Binding Cassette Transporters
  • Adenosine Triphosphate

Grant support

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.