NMR investigation of the multidrug transporter EmrE, an integral membrane protein

Authors


  • Correspondence to H. Kessler, Institut für Organische Chemie und Biochemie, Technische Universität München, Lichtenbergstrasse 4, D-85747 Garching, Germany

  • Fax: +49 89 28913210.

  • E-mail:kessler@artus.org.chemie.tu-muenchen.de

  • URL:http://www.org.chemie.tu-muenchen.de

  • Abbreviations. 2D and 3D, two- and three-dimensional; EmrE, Escherichia coli multidrug resistance protein E; HSQC, heteronuclear single-quantum coherence; T2, transverse relaxation time; TM, putative transmembrane helix; Myr2GroPCho, dimyristoylglycerophosphocholine; solvent A, chloroform/methanol (1 : 1, by vol.).

Abstract

EmrE is an Escherichia coli multidrug transport protein that confers resistance to a wide range of toxicants by active transport across the bacterial cell membrane. The highly hydrophobic polytopic integral membrane protein has been purified and studied in its full-length form by high-resolution NMR spectroscopy in a mixture of chloroform/methanol/water (6 : 6 : 1, by vol.). Full activity is maintained after reconstitution of the protein into proteoliposomes from this solvent mixture. A series of heteronuclear (1H-15N) two- and three-dimensional experiments, as well as triple resonance experiments, were applied to the 110-residue protein and led to the assignment of the 1H, 15N and a large part of the 13C backbone resonances as well as many of the sidechain resonances. A preliminary analysis of the secondary structure, based on sequential NOE connectivities, deviation of chemical shifts from random coil values and 3JNH-Hα coupling constants supports a model where the protein forms four α-helices between residues 4−26 (TM1), 32−53 (TM2), 58−76 (TM3) and 85−106 (TM4). For the residues of helices TM2 and TM3 a significant line broadening occurs due to slow conformational processes.

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