Direct Evidence for Substrate-induced Proton Release in Detergent-solubilized EmrE, a Multidrug Transporter

Misha Soskine, Yoav Adam, Shimon Schuldiner*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

53 Scopus citations

Abstract

A novel approach to study coupling of substrate and ion fluxes is presented. EmrE is an H+-coupled multidrug transporter from Escherichia coli. Detergent-solubilized EmrE binds substrate with high affinity in a pH-dependent mode. Here we show, for the first time in an ion-coupled transporter, substrate-induced release of protons in a detergent-solubilized preparation. The direct measurements allow for an important quantitation of the phenomenon. Thus, stoichiometry of the release in the wild type and a mutant with a single carboxyl at position 14 is very similar and about 0.8 protons/monomer. The findings demonstrate that the only residue involved in proton release is a highly conserved membrane-embedded glutamate (Glu-14) and that all the Glu-14 residues in the EmrE functional oligomer participate in proton release. Furthermore, from the pH dependence of the release we determined the pK of Glu-14 as 8.5 and for an aspartate replacement at the same position as 6.7. The high pK of the carboxyl at position 14 is essential for coupling of fluxes of protons and substrates.

Original languageAmerican English
Pages (from-to)9951-9955
Number of pages5
JournalJournal of Biological Chemistry
Volume279
Issue number11
DOIs
StatePublished - 12 Mar 2004

Fingerprint

Dive into the research topics of 'Direct Evidence for Substrate-induced Proton Release in Detergent-solubilized EmrE, a Multidrug Transporter'. Together they form a unique fingerprint.

Cite this